I use a hilux sized battery from a bus

760 CCA and it will run my 40 liter engel for 2 days without charging and still start. The only thing I would do diffently with this set up is rotate the battery so the positive is near the firewall cause i've had to insulate the bonnet to stop it burning! Also just need to upgrade the earth to something a bit bigger then the standard pencil p.o.s