Checking the quiescent voltage
Disconnect the cable from the negative battery terminal.
Leave the battery disconnected for at least two hours.
Measure the quiescent voltage using a digital multimeter.
The battery needs to be charged if the resting voltage is below 12.45 V (the charging procedure is described later in this section).
Text taken from the website: peugeotbook.ru
Make sure the battery is charging.
If the charge is normal, check the battery under load.
If the battery does not charge, it may be sulphated. Sulfation means the battery is damaged due to insufficient charging - replace the battery.
Load testing
During this test, the load current should increase to a value at least three times the battery capacity in amperes (A).
For example: a battery with a capacity of 60 Ah must be loaded with a current of 180 A (=3x60).
Read the battery voltage after about 15 seconds - the voltage should be 9.6 V. If this voltage is not reached, there may be an open circuit or short circuit in the battery.
Open circuit: Can be identified, for example, by a rapid drop in voltage to 0V when the battery is under load, or if the voltmeter does not read when connected to the battery - replace the battery.
Short circuit: In case of this fault, the cell or cells that are shorted start to boil - replace the battery.
Self-discharge
Once the battery has been tested and shows no signs of the above faults, set it to self-discharge. If the battery self-discharges without holding a charge for more than two days, this may also indicate a possible short circuit - replace the battery.