My dealer recommended the Defa battery charger system. It can charge indefently because of it's on / off function. I decided to put the Defa battery charger on my car, and now it works fine !

 

If you want to stay low price than you guys nailed it. But if you want the best charger/maintainer on the market in my opinion it's the powermax converter pmbc series. A lot of dealerships use these as chargers and maintainers when there fixing our cars in this shop. Their not that expensive and have a 2 year warranty. I have had mine for over a year I paid about $100 for it. It is perfect but not the cheapest

 

I guess if you park in a parking lot such as myself this is not applicable? I'm going on vacation in June for a week and quiet concerned if my car will start up when I return.

 

I charged my car last night for 4 hours. Not because I had a low battery warning but wanted to see what it does and had a battery charger which I have never used. Not sure if it did anything as it is almost impossible to see the stupid little window. I can see it is clear but not green, black or yellow. Hmm....
My wife said why in the earth a 2 year old car would need its battery charged? She is right as it looked odd to see an E60 with the hood up and wires hanging out of it. Just couple of thoughts. By the way my car fired up after a 3 week vacation. Never locked it just let it sit in the garage. Cheers