Originally Posted by MarkM

I have a small battery charger that I installed in the enine compartment of my car.....its plugged into the same circuit as the block heater...it goes on when the block heater goes on (on a timer...goes on at about 4 am until I leave for work.) When not plugged in, the battery charger leads are isolated from the battery by a relay...but when power goes on, the leads are connected.
The output of the charger is 3 amps @ 12 V....its small, about 2 1/2 inches square. Red LED indicates when charging...when battery is charged, it switches to green..(trickle).
Is this bad to do..I mean charge the battery (warm the battery??) when it is connected to positive and neg. battery leads. I read in one of the posts that a car battery should be disconnected when charging to prevent damage to alternator. The charger i have is designed for battery-in-car charging, but I'm not sure if this could damage the alternator.
Thanks,
Mark