What gage wire do I need

I've done exactly the same thing a couple times. I use #10 wire, which minimizes line drop. On low voltage systems it does no harm to run larger wire for that reason. I also use a breaker in place of a fuse, so when you do have a fault you don't end up with an unknown dead circuit. The breakers automatically reset, and they aren't expensive. Available at auto parts stores. The #10 wire should be good for 30 amperes, so don't go any higher than that with the breaker, or the wire won't be protected. If you are concerned with a minimum sized wire, I'd think a #14 would do the job. The small refrigerator we run draws roughly 6 amps. You'd want to throttle back the breaker to only a 15 amp max if the #14 wire becomes your choice, I would think.

Harold

Very reasonable but I would suggest at least #10, #8 would be better. The following table gives the voltage drop for 10 feet of wire at 10 Amps. Drop is proportional to run and current so 6 Amps would give 6/10 as much drop. Frame grounds tend to be unreliable. I would use two wires from the battery to the outlet (with the breaker in the hot line near the battery). I would guess your run would be about 15 feet so that would need 30 feet of wire. Therefore, for a 6 Amp load with 30 feet of wire, multiply values by 1.8.

Wire size: AWG 14 12 10 8 6 Voltage drop: .253 .159 .100 .063 .040

0.6A@30': .455 .286 .180 .113 .071

While the wire will handle 30A non-destructively, you would loose almost

1 Volt on 15x2 foot run. Some appliances might not like that.

That's half a volt loss, more if a reasonable routing needs more than 30 feet of wire. As you say, probably ok but ... Personally, I like to go heavy on wire size and have yet to regret it. BTW, #8 wire is used for electric stove outlet wiring and might be your cheapest source.

Ted