Battery Sample Approval and Incoming Inspection

The sample is the last cheap moment to change your mind. Everything after it — tooling, production slots, shipping, customs — costs more to undo, and by the time a container arrives, the argument is about who pays rather than what is right. Buyers who skip the sample checks and buyers who check properly tend to be the same people who later describe a supplier as “unreliable” or “solid”, when in many cases the difference was one afternoon of testing.

This is written for importers taking finished packs or complete vehicles, whether the build is standard or follows the custom OEM route.

Key takeaways

Most sample failures are specification failures. Write the electrical, mechanical and environmental requirements – with test conditions – before the sample is built, and get each line confirmed in writing.
Do the physical checks before you connect anything: housing, welds, wiring and strain relief, labelling, connector and pinout. Photograph everything with the serial number in frame.
Capacity: charge on the specified charger, discharge at the stated constant current to the BMS cut-off at room temperature, repeat three times and take the third result.
Approval should be a written record – serial number, measured capacity, resistance or sag, balance spread, temperatures, BMS firmware version and any agreed deviations. That record is what the production batch is compared against.
On a production shipment, sample across the pallet rather than the top layer, expand the sample if anything fails, and settle payment terms at proforma stage rather than when a fault is found.

Before the sample: lock the specification

Most sample failures are specification failures. The sample arrives, it works, but nobody wrote down what “works” means, so the production batch can differ in ways nobody can challenge.

the electrical specification with test conditions — capacity at a stated rate and temperature, continuous and peak current with duration, charge voltage and cut-off. Our guide to reading a spec sheet shows which lines need conditions attached;
the mechanical requirements — dimensions with tolerances, mass, connector type and pinout, mounting points;
the environmental requirements — IP rating, charge and discharge temperature windows, and whether low-temperature charging protection is needed;
the acceptance test method — how capacity will be measured, by whom, and what the pass threshold is;
the documents that ship with the goods — see our export document checklist.

Send that as one document and ask the supplier to confirm each line in writing. It becomes the reference for the sample, for the production batch and, if it comes to it, for the claim.

When the sample arrives: physical checks first

Do these before you connect anything. Physical faults are the easiest to prove and the most common reason to reject a sample outright.

housing condition — cracks, deformation, sharp edges, damaged threads;
welding and busbars — consistent welds, no spatter, no loose nickel strip or screw terminals;
wiring and strain relief — correct gauge for the current, no pinch points, secured against vibration;
labelling — does it carry the chemistry symbol, rating information, serial number and, for the EU market, the crossed-out bin symbol and QR code described in our end-of-life compliance guide;
connectors and pinout — physically and electrically what your harness expects;
internal layout if you open it — cell spacing, retention, insulation, and whether the BMS sensing leads are routed away from the power path.

Photograph everything before and after opening. Photos with the serial number in frame are the most persuasive evidence you will ever send.

Electrical tests worth running

You do not need a laboratory to catch most problems. A programmable load or even the real vehicle, a decent multimeter, a clamp meter and a thermometer get you a long way.

Capacity — charge on the specified charger, then discharge at the stated constant current to the BMS cut-off, at room temperature. Repeat three times and take the third. This is the same method we specify in our warranty terms, which makes the result usable later.
Internal resistance or voltage sag — compare against the cell data or the supplier’s figure. A pack that sags far more than expected usually has a weak cell, an undersized busbar or a poor connection. Our page on capacity grading explains what cell-level numbers should look like.
Self-discharge — charge to a known state, record the open-circuit voltage, leave it a week or two, and measure again. Meaningful drift points to a cell or a BMS with excessive standby drain.
BMS protection behaviour — confirm that over-discharge, over-current and over-temperature protections actually trip, at roughly the thresholds in the BMS specification. Do not attempt to force a fault a safe pack is designed to prevent; ask the supplier to run destructive checks and send video.
Cell balance — if the pack exposes cell voltages, check the spread at full charge and at cut-off. A wide spread means the balancing is too slow or a cell is off.
Thermal behaviour — run the duty cycle it was bought for and log case temperature. Warm is normal; hot enough to be uncomfortable to touch for long is not.

Finally, test it in the application. Bench results do not capture the current spikes of a loaded cargo tricycle on a gradient or the sustained draw of a golf cart doing eighteen holes. If you are specifying for a fleet, run the real route and log it.

Approving the sample, and what to keep

Approval should be a written record, not a message saying “looks good”. Keep the approved sample, or a full set of photographs and test logs if it has to go back, and record:

the serial number of the approved unit;
the measured values — capacity, resistance or sag, balance spread, temperatures;
the firmware or BMS configuration version;
any agreed deviations, and what was said about them.

That record is what a production batch gets compared against. Without it, “different from the sample” is an opinion.

Incoming inspection on a production shipment

The production batch is where consistency matters, and you cannot test every unit. Use a sampling plan rather than intuition: define how many units you will pull, what you will check on each, and what happens if one fails. A simple approach is to inspect a fixed percentage from across the pallet — not all from the top layer — with a rule to expand the sample if anything fails.

On each sampled unit check:

identity — serial numbers present and matching the packing list and the batch grading data;
visual condition as above, with attention to transit damage;
state of charge on arrival — it should be in the range agreed for transport, consistent with the rules in our packaging and marking guide;
open-circuit voltage, and that it is plausible for the stated state of charge;
a short functional test — charge briefly, run the load, confirm the BMS reports;
on at least one unit per batch, a full capacity check against the approved sample.

Documents to match against the goods: test summary and safety data sheet for transport, the batch grading or capacity report, the certificate of conformity or declaration, the serial number list, and anything your market requires for end-of-life registration. If a document was promised at quotation and is missing, raise it now — it is much easier to fix before the goods clear than after.

When to reject, and when to accept with conditions

Not every deviation deserves a container sent back. Separate findings into three buckets.

Reject — safety related: damaged cells, swelling, leakage, evidence of thermal events, missing or non-functioning protection, or documentation that makes the shipment illegal to transport or sell.
Accept with conditions — cosmetic or minor deviations that do not affect function or safety. Agree a credit, a replacement allocation or a corrective action in writing, with a date.
Escalate — measured performance below the agreed threshold. This is a specification breach, and it is where your approved sample record and your written acceptance method earn their keep.

Put the outcome in writing before you pay the balance. Payment terms that release on arrival rather than on acceptance remove most of your leverage, and this is worth settling when the PI is drawn up, not when the fault is found. The same applies to who pays to treat a failed unit — covered in our recycling and end-of-life guide.

Frequently asked questions

How many units should I test from a shipment?

Enough to catch a systematic problem, not enough to be a production line. A fixed percentage drawn from across the pallet is the usual approach, with the rule that any failure expands the sample. Agree the plan with the supplier before the order so the outcome is not negotiated after the fact.

What state of charge should batteries arrive at?

Whatever was agreed, and it should follow the transport rules. For air shipments of lithium ion batteries on their own there is a state-of-charge limit that has to be met at the point of handing over, which is a production decision rather than a packing one — see our packaging and marking guide.

Can I test capacity without laboratory equipment?

Yes, approximately. Charge fully on the specified charger, then discharge through the real load or a known resistor while logging current and time, and stop at the BMS cut-off. It will not match a laboratory to three decimal places, but it will tell you whether the pack is within a few percent of what was sold, which is the question that matters.

Should I open a pack to inspect it?

On a sample, yes — and photograph it. On production units, no. Opening a sealed pack usually voids the warranty and can compromise the sealing, so inspect externally and rely on the sample teardown plus the batch documentation for what you cannot see.

What if the production batch performs differently from the sample?

Compare against the written record: the approved sample’s serial number, its measured values and the agreed acceptance method. If a measured value falls below the agreed threshold it is a specification breach. Raise it with the evidence attached rather than a general complaint, and hold payment until the outcome is agreed.

Who pays for inspecting and returning faulty goods?

Agree it in the purchase order. A common arrangement is that the buyer covers inspection, the supplier covers replacement parts and freight for valid claims, and returns are handled under a return authorisation. Where a failed unit is regulated waste, treatment and documentation costs also need an owner — see our end-of-life compliance page.

If you want the acceptance method written into a quotation before you order, send us the application, the duty cycle and the target market. We will state what we will measure, at what rate and temperature, and what the pass threshold is — so the same numbers appear on the PI, the packing list and the warranty. Message us on WhatsApp to start.