Autor: Peilin Zhang, Title: Senior R&D Manager, Company: Phonix Technology,
WhatsApp: +86 -135 3039 5151, E-mail: [email protected]
A charger usually shuts off early for one of two very different reasons: it has reached its programmed charging termination condition, or the charging system has detected a condition that requires charging to stop. The important part is determining which one is happening before replacing the charger.
This distinction matters because a charger that stops at the correct point is working normally, while a charger that stops because the BMS has opened the charging path, a battery cell has reached a protection threshold, the charger has overheated, or the charging voltage is incorrect has a completely different problem.
In other words, “the charger stopped” is a symptom, not a diagnosis.
The most useful way to troubleshoot an early shutdown is to look at the complete charging system: the charger, battery, BMS, cable, connector, connected load, temperature, charging profile, and operating conditions.
What Does “Shut Off Early” Actually Mean?
Before troubleshooting, it is worth defining what “early” means.
A user may say that the charger shuts off early because the battery indicator still shows 50%, because the equipment cannot run for as long as expected, or because the charger changes from charging to standby much sooner than expected.
Those observations do not necessarily mean the charger has stopped at the wrong point.
For example, a lithium-ion charger normally operates in constant-current and constant-voltage stages. Once the battery reaches the programmed charging voltage, the charger changes from constant-current operation to constant-voltage operation and the charging current gradually decreases. The charging cycle can then terminate when the selected end-of-charge condition is reached. This type of CC/CV behavior is a normal part of lithium-ion charging. Analog Devices’ explanation of lithium-ion charge termination describes this transition and the use of a low-current threshold or safety timer to end a charging cycle.
That means a charger can legitimately stop supplying significant current even though the battery has not behaved the way the user expected.
There is another possibility: the battery may really not be fully charged, and the charger may have stopped because the BMS, temperature protection, battery condition, or another system-level condition interrupted charging.
These two situations should never be treated as the same fault.
When Is an Early Shutdown Actually Normal?
The first question should be simple:
Did the charger reach its intended charging termination condition?
If the answer is yes, the charger may be operating correctly.
For a lithium-ion charging system, the typical process is:
Constant Current → Constant Voltage → Reduced Charging Current → Charge Termination
During constant-current charging, the charger supplies a controlled current while battery voltage rises.
When the battery reaches the programmed maximum charging voltage, the charger changes to constant-voltage operation. The charger holds the voltage while the battery current gradually falls.
The charger may then terminate charging when the current falls below a programmed threshold, when a safety timer expires, or according to another control strategy defined by the charger and battery system.
Different charger architectures use different termination methods. Some monitor charge current; some use timers; some use battery voltage and recharge thresholds; intelligent systems may also use information from the BMS.
Therefore, there is no universal rule such as “the charger must continue charging until the battery has been connected for X hours.” Charging time depends on battery capacity, initial state of charge, charging current, chemistry, temperature, battery condition, and the actual charging algorithm.
This is one reason why a charger stopping earlier than a previous charging cycle does not automatically indicate a defective charger.
Why Can the Battery Still Appear Not to Be Full?
This is where the diagnosis becomes more interesting.
A charger determines when to stop based on electrical and control conditions. A battery indicator, fuel gauge, equipment display, or user’s estimate of remaining capacity may be based on something else.
For example, a battery can reach the charger’s target voltage relatively quickly because of increased internal resistance or because one cell reaches a limiting voltage before the rest of the pack. The charger or BMS may then reduce or stop charging even though the battery’s usable capacity is not what the user expects.
Battery aging can make this more confusing.
An older battery may have substantially less usable capacity than when it was new. The charger can complete its normal charging cycle while the equipment still has a shorter operating time.
In that situation, the charger may be doing exactly what it was designed to do. The problem is the condition or capacity of the battery rather than the charging power supply.
This is why a charger changing to standby or showing a completed-charge indication should not be interpreted by itself as proof that the battery is healthy or that its original capacity has been restored.
If the specific symptom is that the charger changes to green while the battery still appears undercharged, the more focused explanation is covered in why a battery charger can show green while the battery is not fully charged.
Normal Charge Termination and Protection Shutdown Are Different
This distinction is the foundation of troubleshooting.
| Situation | What the charger may do | What it usually means |
|---|---|---|
| Normal charge termination | Stops charging or enters standby | The programmed charging cycle has completed |
| BMS intervention | Output current suddenly falls or disappears | The battery management system has prevented further charging |
| Over-temperature protection | Current is reduced or output shuts down | The charger or battery has exceeded a temperature limit |
| Output protection | Output is disabled | Over-current, short circuit, abnormal load, or another protection condition |
| Incorrect charging profile | Charging terminates at an unexpected voltage or stage | The charger does not match the battery requirements |
| Battery fault | Charging may stop unexpectedly | The battery or one cell may be preventing normal charging |
| Communication fault | Smart charger may stop charging | Required BMS or system communication is missing or invalid |
The timing of the shutdown is often more useful than the shutdown itself.
If the charger always stops when the battery reaches approximately the same voltage, look first at the charging profile and termination settings.
If it stops after roughly the same amount of operating time, especially after the charger becomes hot, investigate thermal behavior.
If it stops at inconsistent battery voltages and the BMS reports a protection event, investigate the battery and BMS.
If it stops immediately when a particular battery is connected but works normally with another compatible battery, the battery side deserves attention before the charger is replaced.
How CC/CV Charging Can Make a Charger Look Like It Stopped Too Soon
For lithium-ion batteries, the constant-current and constant-voltage stages are particularly important.
During the constant-current stage, the charger controls the charging current. Battery voltage rises as the battery accepts charge.
Once the programmed voltage is reached, the charger changes to constant-voltage operation. The voltage remains controlled while current gradually decreases.
This means the current during the final part of charging can be much lower than the charger’s rated output current.
A 5A charger, for example, does not necessarily deliver 5A throughout the entire charging cycle. The 5A rating describes the designed maximum charging current under the specified conditions. It does not mean that 5A should continue flowing until the instant charging terminates.
The falling current is actually an important part of the charging process.
As a practical engineering reference, charger ICs from major power-management manufacturers implement CC/CV charging and use defined current, voltage, temperature, and timer conditions to determine charging status and termination. Texas Instruments’ BQ25628 charger documentation, for example, describes pre-charge, constant-current, constant-voltage, charge-current termination, temperature monitoring, safety timers, and protection functions.
So if someone measures the charger during the final stage and sees the current falling, that alone is not evidence of a fault.
Battery Chemistry Changes the Meaning of “Shut Off Early”
One of the easiest mistakes in charger troubleshooting is treating every rechargeable battery as if it follows the same charging behavior.
It does not.
Lead-acid, AGM, GEL, lithium-ion, LiFePO4, and NiMH batteries use different charging principles and different methods of determining the end of a charging cycle.
For that reason, the first technical question should always be:
What battery chemistry and configuration is being charged?
Lithium-Ion
Conventional lithium-ion charging commonly uses CC/CV control.
The charger first supplies controlled current. When the battery reaches the specified charging voltage, the charger transitions to constant-voltage operation and current falls.
Charging termination is therefore closely related to the final voltage, current threshold, timer, and battery protection conditions.
A charger designed for one lithium-ion cell count should not simply be applied to a different series configuration because the nominal battery voltage looks similar.
For example, the charging voltage for a 3S lithium-ion battery is determined by the cells in series and the cell chemistry, not merely by calling the battery a “12V battery.” The same principle applies to higher-voltage packs.
If the charger voltage does not match the actual battery configuration, early termination can be expected because the charger may reach its programmed voltage before the battery system has reached the intended state of charge.
LiFePO4
LiFePO4 batteries also require a charging profile appropriate to their chemistry.
A LiFePO4 pack should therefore not be treated as interchangeable with a conventional lithium-ion pack simply because both are lithium-based batteries.
The number of cells in series determines the required charging voltage. BMS behavior, cell balancing, temperature limits, and charging-current requirements can also influence how the charging cycle ends.
This becomes particularly important with larger multi-cell packs, where the total pack voltage alone may not reveal what is happening inside the battery.
For a deeper explanation of this charging behavior, see LiFePO4 battery charger characteristics and charging logic.
It is also useful to understand the engineering differences between lithium chemistries rather than assuming that one lithium charger can serve every battery. The differences between lithium-ion and LiFePO4 charging algorithms explain why the two should be treated as separate charging requirements.
Lead-Acid, AGM and GEL
Lead-acid charging behaves differently from lithium charging, particularly during the later stages of charging and when a battery remains connected to a charger for an extended period.
Depending on the battery type and application, charging may involve bulk, absorption, and float behavior rather than simply stopping at the same type of low-current threshold used by a lithium charger.
This matters when diagnosing an apparently early shutdown.
A charger intended for a 12V SLA, AGM, or GEL battery must have an appropriate voltage profile for that battery. A charger intended for lithium-ion or LiFePO4 should not be substituted simply because the nominal voltage appears similar.
For example, a 48V lead-acid system does not normally use a charger whose output is simply “48V.” The actual charging voltage is higher than the nominal battery voltage. The appropriate charging voltage also depends on the battery type and charging stage.
The relationship is explained in the explanation of why 48V lead-acid batteries require a higher charging voltage.
For a general comparison of battery voltage and charger selection, the guide to choosing a charger voltage for a 48V battery is also relevant.
NiMH
NiMH charging should not be analyzed using the same simple assumptions used for lithium-ion CC/CV charging.
Nickel-based batteries use different charge-detection methods, and temperature behavior and voltage response can play an important role in determining when charging should stop.
That means a charger shutting off “early” on a NiMH system needs to be evaluated according to the actual NiMH charging algorithm rather than a lithium-style voltage threshold.
The BMS May Be the Device That Actually Stopped Charging
In a battery system with a BMS, the charger is not necessarily in full control of the charging path.
The BMS may monitor individual cell voltages, pack voltage, current, temperature, and other conditions. If a protection threshold is reached, the BMS can prevent further charging.
From outside the system, this can look exactly like a charger shutdown.
For example, suppose a multi-cell lithium battery is being charged.
The charger sees the total pack voltage rising normally. However, one cell is reaching its upper voltage limit faster than the other cells.
The BMS detects the cell condition and opens or disables the charging path.
The charger now sees an abnormal or disconnected load and may stop its output.
The user sees only one thing:
The charger stopped.
But the root cause is actually inside the battery pack.
This is why checking only the charger output is sometimes insufficient.
For intelligent charging systems, the relationship between the charger and BMS is important enough that the charging system should be designed as an integrated control system. Phonix’s technical explanation of why a smart charger needs to be compatible with a BMS covers this relationship in more detail.
Cell Imbalance Can Cause a Charger to Stop Before the Pack Looks Full
Cell imbalance is one of the most misleading causes of early charging termination.
Consider a battery pack made from multiple cells in series.
The charger controls the total pack voltage, but the BMS can see individual cell voltages.
If one cell reaches its upper limit before the others, the BMS may have to restrict or stop charging to protect that cell.
The total pack voltage can therefore look reasonable while the individual-cell condition is not.
This creates an important troubleshooting rule:
If a multi-cell lithium battery repeatedly stops charging before expected, measure the individual cell or cell-group voltages if the BMS architecture allows it.
A total-voltage measurement alone can hide the problem.
Battery Aging Can Make a Normal Charger Look Faulty
A battery’s electrical behavior changes as it ages.
Internal resistance can increase, usable capacity can decrease, and cell-to-cell differences can become more pronounced.
One consequence is that the battery voltage may rise to the charger’s target more quickly than it did when the battery was new.
The charger may then enter its normal voltage-controlled stage and eventually terminate charging.
But the battery may still provide much less runtime than it used to.
From the user’s perspective, the charger “shuts off early.”
From the charger’s perspective, the programmed electrical conditions were satisfied.
This is why runtime should not be used as the only indicator of charging completion.
If the battery used to operate equipment for eight hours and now operates for three hours, replacing the charger without checking battery capacity and internal condition may solve nothing.
An External Load Can Also Confuse the Diagnosis
Another common issue is that the equipment remains connected while the battery is being charged.
Suppose a charger supplies 5A to a battery while the connected equipment consumes 2A.
The battery may receive only the net charging current after the system load is taken into account.
If the load changes during charging, the battery current can change even though the charger itself is operating normally.
In a more complicated system, the equipment may also create transient loads that influence charger protection or battery voltage.
This is particularly relevant for industrial equipment, mobility systems, communication equipment, and other products that cannot easily be completely switched off during charging.
Before diagnosing an early shutdown, determine whether the battery is being charged with the normal system load connected.
If possible, repeat the test under a controlled condition with the external load removed.
Cable and Connector Voltage Drop Can Create a False Diagnosis
The voltage measured at the charger output is not always the same as the voltage actually reaching the battery.
There may be resistance in:
- DC cable
- Connector contacts
- Fuse holders
- Switches
- Protection devices
- Crimped terminals
- PCB traces
Under significant charging current, even a relatively small resistance can produce a measurable voltage drop.
For example, if the charging current is 10A and the total resistance between charger and battery is 0.1Ω, the voltage drop is:
V = I × R = 10A × 0.1Ω = 1V
That one-volt difference can be significant in a tightly controlled battery charging system.
A connector with poor contact resistance can also become hot, increasing resistance further and making the problem worse during charging.
Therefore, if the charger voltage appears correct when measured directly at the output connector but the battery voltage behaves differently, measure the voltage at the battery terminals while charging.
The difference between those two measurements can reveal a wiring or connector problem.
Temperature Can Cause Charging to Stop or Current to Be Reduced
Temperature is another reason a charger may appear to shut down unexpectedly.
There are actually two separate temperatures to consider:
- The battery temperature
- The charger internal temperature
The battery may have temperature limits defined by its chemistry and BMS.
The charger may also have thermal protection or thermal regulation.
A smart charger can reduce charging current when its internal temperature becomes too high, while a BMS may prevent charging when the battery temperature is outside its allowed range.
This means a charger that works normally in a cool environment but stops during prolonged operation in a hot enclosure should not be diagnosed in the same way as a charger that stops immediately after connection.
Temperature-qualified charging is a normal design consideration in intelligent battery systems. For example, Texas Instruments’ charger documentation includes battery temperature sensing, thermal regulation, thermal shutdown, and charging safety functions.
For lithium applications, temperature should therefore be treated as part of the charging control system rather than as an unrelated environmental factor.
Communication Loss Can Stop a Smart Charger
In a conventional charger, the charging decision may be based primarily on voltage and current.
In a smart charging system, communication may also be part of the charging process.
Depending on the application, the charger and BMS may communicate through:
- CAN
- UART
- RS485
- Bluetooth
- Another proprietary protocol
The charger may receive information such as:
- Battery voltage
- Charging current limit
- Cell status
- Battery temperature
- State of charge
- Permission to charge
- Fault status
If the charger is designed to require valid BMS communication and the communication disappears, charging may be stopped deliberately.
For example:
Charger → CAN → BMS → Battery
If the charger receives a command indicating that charging is no longer allowed, stopping the output is correct behavior.
If the CAN connection is physically broken, the firmware may also treat the loss of communication as a fault depending on the system design.
This is why replacing a smart charger with a conventional charger can sometimes hide the symptom rather than solve the underlying system problem.
For a more detailed look at this architecture, see how smart battery chargers use BMS communication for charging control.
Incorrect Charger Voltage Is a Common Root Cause
Another basic question is often overlooked:
Is the charger actually designed for this battery?
The label “12V,” “24V,” “36V,” “48V,” or “72V” normally describes the battery’s nominal voltage, not necessarily the charger output voltage required to complete charging.
For lithium batteries, the relationship depends strongly on the number of cells in series and the chemistry.
For lead-acid batteries, the charging voltage is also higher than the nominal battery voltage during charging.
Therefore, selecting a charger only by nominal voltage is not sufficient.
A proper charger selection should consider:
- Battery chemistry
- Number of cells in series
- Nominal battery voltage
- Maximum charging voltage
- Required charging current
- Battery capacity
- BMS requirements
- Charging temperature range
- Charge termination method
- Communication requirements
This is also why questions such as whether a particular charger can be used with a nominally similar battery need to be answered from the actual battery specification rather than the nominal voltage alone.
For example, the discussion of using a 54.6V charger with a 48V battery illustrates why the battery chemistry and configuration must be known before deciding whether a charger is appropriate.
What If the Charger Shuts Off After Exactly the Same Amount of Time?
A repeatable time-based shutdown is a useful clue.
If the charger shuts down after approximately the same amount of time every time, even when the battery state of charge changes, investigate whether a safety timer or programmed charging-time limit is involved.
Time-based termination can be intentional.
A charger may use a timer as a safety mechanism so that a battery cannot remain in an abnormal charging condition indefinitely.
However, if the battery consistently requires more time than the programmed charging cycle allows, the problem may be a mismatch between the charger configuration and the battery requirements.
In that situation, simply increasing the charger current is not necessarily the correct solution.
The charging profile, battery capacity, thermal conditions, and termination logic should be reviewed together.
What If the Charger Shuts Off Immediately?
An immediate shutdown points toward a different group of possibilities.
Check:
- Battery polarity
- Battery voltage
- Output short circuit
- Connector condition
- BMS charge-path status
- Battery protection state
- Charger input voltage
- Communication status, if applicable
If the battery is deeply discharged, some chargers may enter a pre-charge or recovery mode rather than immediately applying full charging current. Other chargers may refuse to charge a battery that falls outside their permitted voltage range.
That behavior is not necessarily a defect.
Battery-charging controllers commonly include battery detection, pre-charge, safety timers, temperature monitoring, and protection functions. These functions exist precisely because the charger should not blindly apply full power to every connected battery.
Texas Instruments, for example, documents dedicated charging behavior for deeply discharged batteries and emphasizes selecting charger protection features according to the application. Its battery charging safety guidance discusses the relationship between charger design, battery condition, and safe charging behavior.
A Practical Troubleshooting Sequence
Instead of replacing parts randomly, troubleshoot the charging system in a fixed order.
Step 1: Record the Battery Specification
Write down:
- Chemistry
- Nominal voltage
- Series cell count
- Capacity
- Maximum charging voltage
- Recommended charging current
- BMS model or specifications, if available
Do not rely only on a label such as “48V battery.”
Step 2: Measure the Battery Before Charging
Measure the battery voltage before connecting the charger.
This establishes the starting condition.
If the battery voltage is already close to the charger’s target voltage, a short charging period may be normal.
If the battery voltage is unusually low, investigate whether the battery is deeply discharged or whether the charger supports the required pre-charge behavior.
Step 3: Measure the Voltage at the Charger
Measure the charger output with the charger operating according to its normal procedure.
Then compare that measurement with the voltage measured directly at the battery terminals.
A significant difference suggests cable, connector, fuse, switch, or contact resistance issues.
Step 4: Measure Charging Current
Watch how the charging current changes during the charging cycle.
If current gradually decreases as battery voltage approaches the target, that may be normal CC/CV behavior.
If current suddenly falls to zero while the battery is far from its expected charging condition, investigate BMS intervention, protection, communication, temperature, or charger configuration.
Step 5: Check the BMS
If the battery has a BMS, check:
- Individual cell voltages
- Pack voltage
- Cell imbalance
- Battery temperature
- Charge MOSFET status
- Protection flags
- Communication status
This step is particularly important for multi-cell lithium battery packs.
Step 6: Repeat the Test Without the External Load
If the equipment can safely be disconnected from the battery during testing, repeat the charging cycle without the external load.
If the charger behaves differently, the connected equipment is part of the charging problem.
Step 7: Check Temperature
Record the battery temperature and charger operating temperature when the shutdown occurs.
Do not compare a cold-start test with a high-temperature test and assume they are equivalent.
Step 8: Check the Charging Profile
Finally, compare the actual charger configuration with the battery manufacturer’s requirements.
Check the charging voltage, current limit, termination threshold, timer, temperature limits, and communication requirements.
At this point, it becomes much easier to determine whether the charger is actually at fault.
A Troubleshooting Table for Early Charger Shutdown
| Possible Cause | Typical Symptom | What to Check |
|---|---|---|
| Normal charge termination | Current gradually falls and charger enters standby | Charging voltage, current threshold, termination logic |
| Incorrect charging voltage | Charging ends before expected state of charge | Battery chemistry, series cell count and charger voltage |
| BMS intervention | Charging suddenly stops | BMS protection status and charge-path MOSFET |
| Cell imbalance | Pack appears undercharged while charging repeatedly stops | Individual cell or cell-group voltages |
| Battery aging | Charger appears normal but equipment runtime is reduced | Battery capacity and internal condition |
| Battery temperature protection | Charging stops only at certain temperatures | Battery temperature and BMS temperature limits |
| Charger thermal protection | Charging stops after prolonged operation | Charger temperature, airflow and installation |
| External load | Battery voltage or charging current behaves unexpectedly | Connected equipment and system load |
| Cable or connector loss | Charger voltage differs from battery voltage | Voltage at charger and battery terminals under load |
| Communication failure | Smart charger stops unexpectedly | CAN, UART, RS485 or other communication status |
| Safety timer | Shutdown occurs after a repeatable time | Configured charging-time limit |
| Output protection | Output disappears suddenly | Short circuit, over-current and abnormal load |
Why Replacing the Charger First Is Often the Wrong Move
When a charger shuts off early, replacing it is tempting because the charger is the component the user can see.
But the charging system is a chain.
Charger + Battery + BMS + Cable + Connector + Load + Temperature + Charging Profile + Operating Conditions
A fault anywhere in that chain can produce a similar symptom.
Replacing the charger without measuring the battery can therefore produce an unnecessary replacement while leaving the real problem untouched.
For example:
- A weak battery can make the charger reach its voltage limit too quickly.
- A high cell can cause the BMS to stop charging.
- A poor connector can create excessive voltage drop.
- An external load can consume part of the charging current.
- A hot enclosure can trigger charger thermal protection.
- An incorrect charging profile can cause early termination.
- A lost CAN connection can make a smart charger stop intentionally.
Only after these possibilities have been checked does it make sense to conclude that the charger itself is defective.
When the Charger Really Is the Problem
There are situations where the charger should be investigated directly.
For example, if the charger:
- Stops at an incorrect output voltage
- Terminates at inconsistent conditions with a known-good battery
- Overheats under a normal specified load
- Cannot maintain its specified charging voltage
- Produces unstable output
- Enters protection without an external abnormal condition
- Fails communication requirements despite correct wiring and protocol
then the charger itself may need further testing.
For engineering evaluation, it is useful to reproduce the problem with controlled variables rather than simply observing the charger in the field.
A known-good battery, controlled load, calibrated measurement equipment, and controlled temperature can help separate charger behavior from battery-system behavior.
Why This Matters More in OEM Battery Systems
For a consumer replacement charger, a simple voltage and current match may sometimes be sufficient.
For an OEM product, the situation is usually more complicated.
The charger may need to match a specific battery configuration, BMS, enclosure, connector, communication protocol, thermal environment, and operating sequence.
The charging system may also need different behavior during:
- Normal charging
- Battery insertion
- Deep discharge recovery
- High-temperature operation
- Low-temperature operation
- BMS protection
- Communication loss
- Charging completion
- Standby
- Fault recovery
That is why an OEM charger cannot always be specified simply as “48V, 5A.”
The important specification is the behavior of the complete charging system.
For systems where the charger and BMS must operate together, custom battery charger and BMS integration is a more appropriate engineering approach than treating the charger as an isolated power supply.
The same principle is described more broadly in system-level charging design versus component-level charging: the charger should be evaluated according to how it behaves within the complete system.
What Phonix Engineering Experience Changes in the Diagnosis
In practical charger development, an early shutdown is rarely investigated by looking at the charger alone.
The first questions are normally about the complete electrical system:
- What battery chemistry is being used?
- How many cells are connected in series?
- What is the required full-charge voltage?
- What is the normal charging current?
- What does the BMS allow?
- Is communication required?
- What happens when one cell reaches its protection threshold?
- What happens when battery temperature changes?
- Is there a load connected during charging?
- What voltage actually reaches the battery?
- What is the intended charge termination condition?
These questions determine the charging behavior far more accurately than the charger label alone.
Phonix develops smart battery chargers for different battery chemistries and applications, including customized charging voltage and current, charging profiles, protection functions, BMS communication, connectors, enclosures, and system-level charging requirements.
That engineering approach is particularly relevant when a customer reports a symptom such as “the charger shuts off early” without initially knowing whether the charger, BMS, battery, or system configuration is responsible.
What You Should Remember Before Replacing the Charger
A charger shutting off early does not automatically mean that the charger has failed.
The most important distinction is whether the charger has reached a normal charge-termination condition or whether charging has been interrupted by a protection or system condition.
For lithium-ion systems, watch the transition from constant-current to constant-voltage operation and observe what happens to charging current near the end of the cycle.
For LiFePO4 systems, verify the cell configuration, charging voltage, BMS behavior, cell balance, and temperature conditions.
For lead-acid, AGM, and GEL systems, verify that the charger uses the appropriate charging stages and voltage levels rather than applying a lithium-style charging assumption.
For NiMH systems, use the appropriate nickel-based charge-detection method rather than judging the charger by lithium charging behavior.
For smart battery systems, check BMS status and communication before assuming that the charger has shut down by itself.
And for any system, measure the voltage and current at the battery as well as at the charger. Cable resistance, connector losses, external loads, and temperature can all change what the charging system actually sees.
The most useful conclusion is therefore not simply “the charger shut off early.”
It is:
“The charging process stopped at this voltage, current, temperature, or system condition — and this is what caused the charger or BMS to terminate charging.”
Once that condition has been identified, the difference between a normal charging cycle and a genuine charging-system fault becomes much easier to see.
