BMW E87 battery drains or won't charge
Why does the E87 battery drain overnight?
One typical cause is a badly corroded ground cable under the engine. A corroded or broken battery cable in the boot (trunk) pass-through can also prevent starting. Check the cables and connections first and protect the cleaned connections with petroleum jelly.
How can I tell if the E87 is charging the battery properly?
With the engine running, the charging voltage should be about 14 V. If the measurement shows less than 13 V, the car is not charging properly. With the engine off, you can watch whether the resting voltage drops clearly within about a quarter of an hour.
Does a new battery need to be registered on the E87?
It depends on the car. If the car has an IBS battery sensor (a sensor that monitors the battery's condition), the new battery must be registered with ISTA (BMW's service software), because it affects the charging voltage. A 2005 120d had no sensor, and registration was not required.
How do I charge an E87 with an IBS sensor using an external charger?
The IBS sensor is on the battery's ground cable. Therefore the charger's negative lead is connected to the body ground bolt and the positive directly to the battery's positive terminal, not to the battery's negative terminal.