Originally Posted by 1fastdoc
I hear several people saying that using a battery tender makes a difference but I don't see how. I assume you mean driveability.
I have an '11 M3 with a little over 8k miles on it. I drive 1.6 miles to work. 2.9 miles to the gym and then 1 mile back home. This is 5 days/week plus a few miles on the weekends.
So far it still starts fine, the lights are bright, the stereo is loud, the heated seats keep my ass warm, etc.
With prior cars when the battery goes bad it won't start. What's different with the M3?
The life expectancy of the battery is better if you keep it charged to top levels instead of running it down to almost dead. It is a small price to pay(time/effort) to keep the battery performing longer before it has to be replaced.