00 00... Battery: checking display (magic eye), recharging battery if necessary
If a battery is replaced, it is absolutely essential to choose a replacement battery of the same capacity/size. Lead-calcium batteries may only be replaced by another lead-calcium battery or an AGM battery.
Poorly charged batteries are susceptible to freezing.
Flat batteries incur preliminary damage if the open-circuit voltage is less than 12.0 V. This can cause premature failure.
Storage temperatures above 35°C speed up the rate at which a battery will self-discharge.
If electrical loads/consumers in the car are switched on in the course of maintenance or service-inspection work, this current drain must be compensated for by connecting a BMW-approved charger.
During each service-inspection or battery check, observe the color of the hydrometer and proceed as follows:
Green = Battery sufficiently charged (no action necessary)
Black = Battery insufficiently charged (charge battery fully)
Bright yellow = Acid level too low (replace battery)
Checking battery:
A fully charged, as-new battery has a voltage of at least 12.7 V.
Depending on the battery voltage, proceed as follows:
- If the battery voltage is over 12.3 V, no further action is necessary.
- If the battery voltage is between 12.0 and 12.3 V, charge the battery for at least 12 hours.
- If the battery voltage is below 12.0 V, the battery has incurred preliminary damage and must be replaced.
On a battery which has been stored, the color of the hydrometer (the so-called "magic eye") can remain black although the battery has an open-circuit voltage value of at least 12.7 V. This is caused by acid lamination in the battery. Such batteries are nevertheless fully charged and OK.
To eliminate acid lamination, slowly turn the affected battery over once. This causes the magic eye to show "green" again.
It is necessary to wait at least 6 hours to be able to correctly determine the open-circuit voltage. Only after this period has elapsed should you proceed to ensure that possible surface charges which could distort the measured voltage value are eliminated.