Also, with the rear door window opening separate from the door, and the sun roof, I will have plenty of circulation in the hot weather. I've also got plans for a cooling fan in one of the side, rear windows.

The only addittional advice I have been given about the marine battery is to make sure you vent it to the outside. No problem in the back of a pickup but more so in the back of an enclosed vehicle.

It generates hydrogen gas while charging.

Enough of it that I have been told it could be problematic (if not vented)

Good point Nancy. ALL auto batteries need to have air circulation of some sort.

Old thread but I am deciding to install 2nd battery this year.

Now considering an AGM** sealed 12Volt that does not require ventilation and trying to figure out as much as I can before I look at installing it.

Found two 10 inch box fans that throw a LOT of air - are AC but use a 12volt transformer - or - D cells, so if I go directly to the 12 volt with a plug of proper polarity should be good .each fan is rated at 0.6amp. and I want to also run a computer and printer which I gather will have to go through an inverter as the output of the transformer is 20V, 3.5 amp

Trying to figure out the size of the 2nd battery (as the bigger the battery the more it costs...and I am sure there are power losses with the inverter and the battery isolator)

The math is getting, well..... a bit much.....

Anyone know of good sites for how to figure this out? I don't want to spend too much money and have way more than I need and too little and not have enough.

**The glass mat batteries seem to SIGNIFICANT safety advantages over the lead acid and since it will HAVE to be in my SUV (albeit in a plastic strapped down box) I would prefer to be that way......

Is there an expert on all this on the board or any good how to articles......

Another option is D cell rechargeables but it would take 16 to run two fans and at the cost for these I am approaching the deep cycle battery option that gives me more capability and automatic charging and takes care of the computer issue.