I have a small "Battery Tender" for my motorcycle battery. It looks just like a regular A/C adapter but has a LED on the front. It's red when charging and Green when it's in "trickle" or maintenance mode. Does this sound like what you have? I'm sure you could use this on a car, but car batteries are much more stable than the small sealed gell cell batteries in motorcycles and ATV's. I also use my car almost daily.

Using this charger, I've never removed a battery from my motorcycle in the winter and have gone 30,000 miles and 4 years without any problem with the OEM battery.