Another thing to consider is the type of battery and condition. I run 2 6 VDC golf cart batteries in series and before I head out, I put them in my garage and charge them with a heavy duty charger. It takes pretty much all day of charging for them to get full so depending on your drive, you may not be getting a full charge on them. I run Energizer EGC2 batteries and they last me almost a week of dry camping.

Energizer GC2 (6V battery)
SAM'S CLUB

Amp-Hour at the 20 hour rate: 225Ah
Minutes at 75 amps: 110 minutes
Minutes at 25 amps: 447 minutes

since I'm using two, double the times shown above. So if you are running a refrigerator, inverter, smoke detector, co2 detector, you are drawing 2 amps plus lights when they're on another 1 amp ( not on all day). You should be good for a LONG time with fully charged batteries.

447 minutes at 25 amps becomes 447x(25/3), so for for 3 amps = 3725 minutes per battery. Times 2 batteries and you should be good for 5 days.