Changing the battery in an M6

[andrewsedward]

I own a 2005 M6 and quite often use it for short journeys. A few times now it has shown the message saying that it has had increased battery discharge. I am thinking that I need to change the battery so wanted to know if anyone can tell me if I should go for a 110Ah battery or go for the 90 Ah AGM battery. Also, a mechanic that is doing some other bits on the car has said he thought that BMW need to be doing the battery change because the car needs to be programmed for a new battery. Does that make any sense to anyone?

[MFunf]

I had to disconnect my battery (M5) and was also nearly fooled by the warning near the battery about re-programming functions etc. Basically other than time and date everything was fine.

[E30M3SE]

Believe the reprogramming is only required if you change the Ah of the battery, replacing like with like should not cause any issues.

[andrewsedward]

Thanks to both the above. I have read that a more relevant battery for short journeys is the 90Ah AGM battery, which I think is different to what's in there now, so it may need some sort of reprogramming. Maybe I'll just go for a 110Ah one and save the hassle.