Deep cylce batterys take longer to charge but will power devices for longer also. You can set a 'dual battery' system in your car, so once your starting battery is charged, the alternator starts charging the deep cycle one. Or you can just charge it before you go, but depending on what your running i cant imagine even the best batteries going for more than a couple of days. Also, you dont want to discharge your batteries more than 50% as it's bad for them and shortens their life.
Youcould invest in a small generator - noisy, and smelly, and bulky unless your spending big bucks. A solar charging setup, expensive, a possiblty a bit bulky, but a good investment in the longrun once set-up. Or as I said already, run 2 batteries in your car and meter the deep cylce used for camping accesories. Once its getting low go for a 1/2hr drive to see the sights
Life's too short to be grumpy, SMILE
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