Battery Charging
The purpose of charging a battery is to put back the energy that has been removed. A battery that is not properly charged will deliver sub-standard performance and display a shorter life span.
A battery should be charged only after performing a visual inspection on the battery case and the electrolyte levels. Never attempt to charge a battery with a damaged case or low electrolyte levels.
A state-of-charge test should be performed before attempting to charge a battery.
Unplug the charger or turn it off before disconnecting the leads at the battery.
The best charging method is to SLOWLY recharge the battery using the BMW approved battery charger. A slow charging rate allows more time for the electrolyte to penetrate the plates.
Batteries that are fully discharged should be charged according to the following table.
| Reserve Capacity Rating (RC) | Slow Charge | Fast Charge |
|---|---|---|
| 80 minutes or less | 15 hours @ 3 amps | 2.5 hours @ 20 amps |
| 80 - 125 minutes | 21 hours @ 4 amps | 3.75 hours @ 20 amps |
| 125 - 170 minutes | 22 hours @ 5 amps | 5 hours @ 20 amps |
| 170 - 250 minutes | 23 hours @ 6 amps | 7.5 hours @ 10 amps |
| above 250 minutes | 24 hours @ 10 amps | 6 hours @ 40 amps |
Workshop Hint
Electrolyte levels may drop at a higher rate in the winter months, due to higher loads and increased utilization of electrical systems.
Workshop Hint
Many battery problems are caused by loose or corroded connections. Insure that cables are free from corrosion and tight before continuing diagnosis.