[m@rco]

My car's (E90 328i MT, manuf date 11/2006) first battery is starting to show signs of weakening. A few seconds after switching off the car, the amber battery light comes on. Also, when parked with the parking lights on, the amber light will come on after about 20 seconds. Radio etc. will also no longer stay on when the car is fully switched off. Not too bad a performance after almost 8 years...

The dealer quoted me a new 90Ah AGM (Absorbed Glass Mat) battery for €450 (~$600 installed!)... I'm not sure why I am being quoted an AGM battery. I don't have one now.

My dad's E39 528i has a 70Ah battery for basically the same 3-liter engine. Given the relative mild climate where I live (and the occational skiing trip in the cold Alps), I'm considering to buy a 70Ah for my car now. Internet price for a German, quality brand, Varta battery including shipping is ~€135 ($180).

Anyone experience with downgrading from a 90Ah to a 70Ah battery?

I plan to install the new battery myself. And I will have the battery registered at the dealer (~$50). Will the 15-min ride from home to the dealership harm the battery (charging program is not set for 70Ah yet)?

Thanks for the advice!