There were 5 battery types fitted to the 6 Series:
- Regular lead acid 80Ah, 90Ah & 110Ah
- AGM 90Ah & 110Ah
The charging system in the car is designed to use these ratings only so fitting a 100Ah for example might cause problems because the car's power management system does not have a charging profile to match it.
Important points to note:
1. When you change a battery you must "register" it to the car. Over time that power module changes its charging profile to counteract the deterioration in the battery. Registering the new battery means the power module gets reset to provide the appropriate charging that a new battery needs rather than the higher demand that an older battery would need. Failure to register a new battery will shorten the life of your new battery. If you do not register the battery you won't notice anything in the short term but within a few months to a year the battery may be damaged due to overcharging.
A battery can be registered using DIS software or Autologic, possibly others too. A good independent mechanic should have the right equipment to do this. Check out your local specialists to see who can do it. Any specialist who says that it is not needed does not know what they are talking about, go somewhere else.
2. If you change the battery to one with a different rating or change from regular lead acid to AGM then you also have to tell the car that this change has been made, again, it's all to do with the charging profile. Again this is done with software.
If your car has the OEM battery still then you can tell what battery is correct for your car by reading the 11 digit part number on the top. If it is the OEM battery & it is white it has a regular lead acid battery, if it is black it has an AGM battery. Most guys would recommend switching to the (more expensive) AGM battery because of the demands placed on a battery in the e63. Especially if you do lots of short journeys, the AGM battery is a deep cycle battery which means it can cope better with frequent high discharge & charging cycles.
Finally these cars do not like short journeys, they use a lot of power when starting up & therefore need a suitably long period of running to replenish the discharge. With short journeys this can't happen. BMW refer to this as an "unfavourable driving profile", for cases like this they recommend keeping the car on a trickle charger for the battery.