Recharging a battery

I know nothing about batteries and charging them. I have read that you can't count on the TV to keep them charged, and to watch out for buying bigger heavier batteries because of the weight. I am most concerned about the heater fan. In air condition weather we would be at an electrical hook up campsite. DW does not do well in hot weather with out air conditioning so I don't go there. Having camped at Yellowstone in the summer in a tent with frost on the picnic table in the morning, I would like not to be as cold as we were in that tent. With a several day trip to Yellowstone, what would you do to maintain battery charge, and how long could I stay with no electrical hookup if the main power drain was the heater fan? How long does it take to recharge the battery or batteries at an electrical hookup site?