Checking Charge State Of A Lithium-Ion Battery Using A Battery Tester

Information 

Charging a 12 V lithium-ion battery that has become totally discharged:

When a lithium-ion battery reaches an open-circuit voltage < 12.5 V or a charge state < 15%, a protection relay in the battery opens.

To recharge a lithium-ion battery that has become totally discharged, apply a voltage of 11 V - 14.4 V to the external power connection in the vehicle (at the battery terminals if the battery is removed) for at least 30 seconds using a backup battery or connect a charger in backup mode. The protection relay closes (short clicking sound can be heard in the lithium-ion battery).

The lithium-ion battery must then be charged fully with 14.4 V.

1. Check the battery charge state according to the operating instructions for the relevant quick-start battery charger.

   Evaluating the test results and subsequent procedure: 

   Open-circuit voltage in volts	Charge state in %	Evaluation and procedure
   13.7 - 13.4	100 - 80	Charge state OK
   13.4 - 13.25	80 - 50	Charge state reduced; recharge battery.
   13.25 - 12.5	50 - 15	Battery discharged; recharge battery.
   < 12.4	< 15	Battery totally discharged; it might be possible to recharge it. Close protection relay, recharge battery.

   If the protection relay does not close, replace the battery

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