A voltage reading is a useful first check, but it cannot tell you how much charge a lithium-ion battery will deliver. Capacity testing measures that charge; load testing helps investigate voltage drop or shutdowns while the battery is powering equipment.
The examples in this guide focus on finished LiFePO4 packs for energy storage, including Techfine’s LP series. We assemble these batteries and supply them for private-label projects, so we also cover how business buyers can check a delivery.
We’ll identify the battery and prepare the test, then work through voltage, capacity, load and storage checks. The final section shows how to record the results for incoming inspection.
Before you connect a tester
Identify the battery’s chemistry, model and rated voltage from its label and documentation. A single cell, a small equipment battery and a finished storage pack need different connections and test settings. A pack’s external terminals may also be controlled by a battery management system (BMS).
This guide covers checks at accessible pack terminals and through the product’s approved display or monitoring interface. Keep the enclosure closed and the protection system active. For an embedded battery or an unfamiliar high-voltage system, use the equipment’s service procedure and a qualified technician.
Before a normal electrical test:
- Check for swelling, leakage, damaged terminals, abnormal heat or other visible damage. Stop and follow the manufacturer’s safety procedure if any are present.
- Check the battery’s permitted charging and discharging conditions, including temperature. Identify the settings needed for the particular test; a product’s maximum ratings do not define a complete test procedure.
- Use instruments, leads, cables and protection suitable for the pack and installation. Have a qualified technician arrange charging and load tests, with a clear way to stop the test.
Choose the test for your question
You do not need to run every test on every battery. Start with the symptom or the decision you need to make.
| Your question | Start with | What the result helps establish |
|---|---|---|
| Does the battery have an unexpected output voltage? | Terminal voltage and protection status | Whether the external output needs further investigation |
| Does it deliver the expected amount of charge? | Controlled capacity test | Delivered Ah under recorded conditions |
| Why does equipment shut down when a load starts or increases? | Load test and connection checks | Where voltage falls and what ends operation |
| What changed while the battery was stored? | Comparable before-and-after records | Whether temperature, remaining loads or battery behavior need investigation |
An internal-resistance reading can add diagnostic information when measured by an appropriate method. It does not replace a capacity test or provide a remaining-life percentage by itself.
Check voltage with a multimeter
For a resting measurement, isolate the charger and loads using the installation’s procedure. Keep the pack’s output enabled if its terminal-test procedure requires it, and record whether it is on, asleep or showing a protection indication.
Use the meter’s DC voltage function and voltage input:
- Plug the black lead into COM and the red lead into the voltage input, commonly marked V/Ω. Select DC volts and a suitable range. Check that the meter and leads are rated for the measurement.
- Touch the red probe to the positive terminal and the black probe to the negative terminal, keeping exposed probe tips clear of adjacent conductors.
- Record the voltage, battery temperature, output status and time since charging or discharging. If the specified procedure calls for a rest period, use it before comparing readings.
Never connect the meter across battery terminals with a lead in an A or mA current input; that can create a short circuit. Do not use resistance mode across an energized battery.
Compare the reading with the documentation for that chemistry and pack. The nominal voltage on the label identifies the voltage class; it is not a pass/fail value that every reading must match.
If the reading is unexpectedly low or zero, check the meter setup and the pack’s output state before concluding that the cells have failed. A battery BMS can disconnect the output during protection. Save any indication and follow the model’s fault procedure; do not bypass protection to obtain a reading.
A normal-looking voltage still leaves the capacity question open. LiFePO4 has a relatively flat voltage curve through much of its operating range, so a small resting-voltage difference is a poor basis for a precise state-of-charge percentage. If the concern is short runtime, move to a controlled capacity test.
Measure capacity under defined conditions
A capacity test measures the ampere-hours (Ah) delivered from a defined starting charge to a specified cutoff. Before testing, write down the charging procedure, any rest period, battery temperature, discharge current and cutoff. Compare the result with a rating established under comparable conditions. If the test settings are missing, establish them with the supplier before using the result for acceptance.
Start by separating capacity from current ratings. The specification for our 12.8V, 100Ah LP battery lists a recommended charging current of 50A and a maximum continuous discharge current of 100A. The 50A figure applies to charging; the 100A figure sets a continuous discharge limit. Choose the capacity-test current from the relevant test procedure, within the model’s operating limits.
Use a battery tester or electronic load rated for the pack’s voltage, current and power, with suitable cables and protection. Program the cutoff before discharge; do not rely on forcing a protection trip to end a normal capacity test.
- Prepare the battery. Follow the charging and rest conditions you recorded. Note the model, serial number and battery temperature.
- Run a controlled discharge. Apply the recorded current and cutoff. Log current, terminal voltage, temperature and elapsed time. Stop if there is abnormal heating, damage or a protection event.
- Record why the test stopped. Save the accumulated Ah and the endpoint. Note whether the tester reached its programmed cutoff, hit an equipment limit or stopped because the battery cut off its output. For the LP model above, also record the display’s status and protection indication. Never bypass protection to extend the test.
For a constant-current discharge, the calculation is straightforward:
Capacity (Ah) = current (A) × discharge time (hours).
If current varies, use the tester’s accumulated Ah reading instead of multiplying one current reading by the whole test time. Energy is a separate quantity, measured in Wh, and depends on voltage as well as current and time.
Suppose a battery labelled 100Ah delivers a constant 20A for 4.5 hours before the agreed cutoff. That is 90Ah, or 90% of the label rating under those test conditions. It does not establish that 90% of the battery’s service life remains, or decide whether it meets your acceptance criteria.
Temperature can change that comparison. A published specification makes the effect concrete: Victron’s LFP-Smart 12.8/100 is rated at 100Ah at 25°C and 80Ah at 0°C, for discharge currents of no more than 1C—100A for that model. Comparing a cold test directly with a room-temperature rating can make the battery appear to have lost capacity. Use the temperature and current conditions specified for the battery you’re evaluating.
If the battery stopped the discharge before the planned endpoint, keep the result alongside the protection indication and follow the model’s fault procedure before deciding whether to retest. Restore the battery to the condition required for its next use or storage, following its charging instructions.
Check performance under load
A load test helps explain what happens while the battery supplies equipment. Set the load within the battery’s continuous and permitted short-duration limits, as well as the limits of the tester, wiring and connected equipment. Use the tester’s current measurement or a suitably rated DC current clamp; do not route a storage pack’s load current through an ordinary multimeter’s current input.
Record the starting charge condition and temperature, then observe battery-terminal voltage, load current and any battery or equipment alarms during the controlled test. To investigate a shutdown, capture the readings immediately before it as well as the indications afterward. Stop if there is abnormal heating or a protection event.
The measurement location matters. Voltage drop in cables and connections is assessed while current flows. A technician can compare battery-terminal voltage with the voltage at the equipment input under the same steady load, then investigate the intervening connections if the difference is excessive for the installation.
- Battery voltage holds, but the equipment input falls: investigate cables, terminals and connections before attributing the problem to the battery cells.
- The battery cuts off its output: preserve the protection indication and compare the load and temperature with the pack’s limits.
- The equipment shuts down while battery output remains available: compare its recorded input voltage with the equipment’s limits, and check its settings and alarm record. If battery-terminal voltage also fell, review the pack’s starting charge, load and operating conditions before assigning the cause.
A brief voltage sag or successful short load test does not tell you how many Ah the battery can deliver. Use the capacity procedure when that is the question.
Check changes during storage
Start with the storage condition specified for the battery and disconnect external loads as directed. Record the date, temperature, terminal voltage and any displayed charge estimate, together with which parts of the battery remain active. Repeat the observations after a defined interval under comparable conditions.
An active BMS, display or connected device can consume charge during storage. A specification for working consumption describes an operating condition; it cannot automatically be treated as the battery’s monthly self-discharge rate. Record the operating mode before comparing two stored packs.
If you need to compare the charge remaining
Voltage and display changes are useful screening observations. For an Ah comparison, establish a baseline before storage and measure what remains afterward:
- Establish the starting baseline. Measure the deliverable Ah at the agreed starting storage condition, using the selected discharge current, cutoff and test temperature. Then restore that starting condition before storage.
- Measure what remains. After storage, discharge under the same test conditions before recharging, then compare the delivered Ah with the baseline.
For a partly charged storage test, using the label rating or full-charge capacity as the baseline would count charge that was never present as a loss. Recharging first answers a different question: how much the battery can deliver after a full charge.
Use the results for incoming inspection
For a delivery, first check that the model, labels and supplied documents match the order. Keep the applicable specification with the record—for LP products, this includes the LP-series brochure—alongside any agreed test settings and acceptance criteria.
Keep each document’s purpose clear. A UN 38.3 test summary concerns transport-related design testing. It does not report the delivered capacity of the particular units you received.
Agree how units will be selected and how their results will determine the decision on the batch. NIST’s description of acceptance sampling makes that distinction explicit: a sampling plan includes both selection and decision rules. Testing one unit does not establish the condition of every battery in the delivery.
Use a record that lets another person understand and, where appropriate, repeat the test:
| Record | Include |
|---|---|
| Battery and sample identity | Model, serial number, shipment or batch reference, and how the sample was selected |
| Preparation | Initial condition, charging procedure, rest time and temperature |
| Equipment and settings | Tester identification, measurement points, current or load, cutoff and temperature limits |
| Results | Voltage observations, delivered Ah and Wh where measured, elapsed time, temperature and alarms |
| Endpoint and decision | Why the test stopped, relevant acceptance criterion, and agreed next action |
For the hypothetical 100Ah battery above, suppose the record shows 20A for 4.5 hours and “tester cutoff reached,” but gives no cutoff setting or battery temperature. You can verify the 90Ah calculation, but you cannot yet establish a comparable result or decide acceptance. Keep the 90Ah result and request the missing settings and temperature record before making that decision.
If the log instead shows a protection event before the planned cutoff, record it as an interrupted discharge and review the fault before considering a repeat test. The stopping reason changes the next action even when the Ah total is the same.
For a distribution or private-label project, share your target market, application, required voltage and capacity, expected quantity and branding needs through our battery project service. Include the intended inverter or load so we can discuss suitable product options and the documents to confirm before ordering.
