Battery tech time

[John]

I'm adding a second battery to the Jeep, mounted in the rear (inside) under a tool box and behind the back seat. I'll use it for extra CCA on starting, to power the rear winch, and to run a power inverter off of it.

Now I get the crazy idea that if there's a 110 outlet in the Jeep then why couldn't I plug my engine block heater up to it? The rear battery is isolated unless the key is on, so it couldn't really hurt I figure.

Since the camper is in winter storage mode, has a perfectly good "deep cycle" battery that's charged up (camper stays plugged in to house) and a power inverter I figured to try a little experiment.

I unplugged the RV from the house so that the battery isn't being charged, I plugged the block heater to the inverter with the battery reading 13.5V and went back inside for 2 hours (hey, wind chill is around -20? or so) and then came back to see how it did.

The battery was down to 11.2V and the inverter wasn't powering the block heater any more, so it seems that it's a question of reserve capacity at this point. So now I'm on the prowl for a dry/gell cell battery that can handle this kind of drain. Anyone have any idea's on a battery up to this? Size isn't really all that much of an issue in this case either.