Battery Test: battery calibration via Service Mode

Description

Battery Test is a BMS diagnostic and calibration procedure: it runs a full discharge-charge cycle and refreshes the capacity/range estimate, showing the battery's real state. Useful after buying a used Tesla and when you suspect battery problems.

The test is not a cure for imbalance: the balancer in the pack is there from the factory and runs constantly on its own (during sleep, on slow charging). If imbalance codes (BMS_a066/a064/a079) persist, the always-on balancing is no longer coping, the cells have degraded, and the test won't "heal" them: at best it temporarily evens out the readings. The fix is a module/pack replacement.

How to run Battery Test

1. Only on a slow charger (Type 2 / Wall Charger), not on CCS.
2. Not at a public station: the test does not run to completion there, because the charger drops the session during the discharge phase, when the draw falls to zero. A real case on EVICA: at about 20% remaining the station shut itself off (#492907, #461586). You need your own (home/garage) or a service charger that doesn't drop the session on pause.
3. Discharge to 2-3%, start the test in Service Mode, wait 12-18 hours.
4. The charger must deliver at least 5 kW.
5. Once every six months is Tesla's limit (the test cannot be run more often), not a recommendation. Run it rarely and only if you suspect a problem: each test is a full discharge/charge cycle for the battery.

Risks and a gentler alternative

Several owners saw an imbalance error show up after the test. The mechanism: a car that has spent its whole life in the 20-80% window goes down to 0 and up to 100 for the first time, and the BMS sees the real per-cell picture for the first time. The test breaks nothing, but it can reveal an imbalance that was not showing before (#492926, #492931, #492932).

If the goal is simply to refresh the remaining-capacity figure (after a battery replacement, for example) rather than to get a test report, a gentler option works: discharge to 1-3% and charge to 100% at a low 3-4 kW from a household outlet (#464013).

The chat also suggests "pulling the imbalance back in" with several slow AC sessions in a row: there is a case where imbalance dropped from 10 to 4 mV after the third one (#480871, #480874). This must not be read as a cure: slow charging simply gives the factory passive balancer time to finish its work, and it is the readings that even out, not the state of the cells. If the imbalance code comes back, the balancer is already losing (see the box above), and the only fix is a module/pack replacement.

Community experience TESLA Belarus

From the TESLA owner's group BELARUS chat: analysis of 400 000 messages.

Who reported the issue: Vitali K, Сергей

Who found the fix: Stinger, SΞDΞK, Dzianis Balyka, AV, Pasha n1claus

Discussion in Telegram: #176501, #259300

Links

• Calibrating the BMS (Tessie Help Center): https://help.tessie.com/article/78-calibrating-the-battery-management-system
• Tesla BMS Calibration (EV Inventory): https://ev-inventory.com/guide/tesla-bms-calibration.php
• Tesla's Battery Health Test (Not a Tesla App): https://www.notateslaapp.com/news/2049/teslas-battery-health-test-see-your-battery-health-in-app-or-in-service-mode