http://www.westmarine.com/mounted-battery-chargers

I'm a boater, and I rely on these kinds of reliable chargers. I not only keep my boats' batteries on these chargers overwinter and in-between boating outings in the summer, but also my other batteries in storage (lawn tractor overwinter, snow machines in summer, as well as my car if I'm keeping it parked for a while on a vacation, etc.).

Yes, they're more expensive than automobile counterparts, but they're also higher quality than most cheaper car chargers. The thing to remember is that, for boaters like me, a reliable battery can be a life-or-death matter when you're miles out in the ocean and need to start your engine when rough seas develop -- it's not the same as waiting, safely parked at the curb in your car, for a AAA truck to come. Not to mention powering your ancillary equipment (refrigerator, lights, VHF radio, etc.) when you're cruising and anchoring for the evening. So you learn how to take very good care of your batteries!