I know I have heard that leaving a charger connected to a battery shouldn't drain it, but I don't want to take any chances, (and I needed something to tinker with at the time) so I mounted relay in the engine compartment (inside a box)....House current clicks the relay "on", and connects BOTH the neg. and pos. leads from the charger to the battery. When I unplug it, both pos. and neg. are disconnected so that the charger is COMPLETELY isolated. (I didn't use a standard Bosch 12V single pole relay....I used a "double pole" 120V relay with blade connectors that plugs into its base...I mounted it onto a piece of oak and covered it with an inverted deep grey plastic wall outlet box, and cut slots for wires. I attached the whole unit to the wheel hump)

(Nice idea with the Radio Shack diodes....more compact than my system!)

I figure that if the battery is good, it really does not need to be on the charger all night....I have the system set up so that the charger and the block heater go on at the same time at about 3 am.

What I am looking for now is a nice small low profile ceramic heater, about 750 watts, that I can mount out of the way in the passenger footwell, and hook it up to the same system so that in addition to heating the engine and charging the battery, the cabin will be nice and toasty in the morning. This does make me a little nervous....I don't want to melt the interior, or worse, set the vehicle on fire. So I am not looking for a cheap $10 piece of crap.

Regards,

Mark

__________________
1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)