I have my 2000 M5 in my garage for the winter. I start it every two weeks just to get new gas thru the injectors. When I went to start it several weeks ago the battery was weak so I put the charger on it. When I went to start it today the battery was not strong enough to turn it over. The battery, I think it is the original OEM battery so it probably is time for it to be replaced. Has anyone had experience with the Optima battery in an M5. Do they have one that fits propery in an M5 without having to make special hold downs or have it flopping around in the battery compartment?