I am using Amped Outdoors 32 amp hour lithium battery . Installed with quick connects (ordered off Amazon )and rigged a plastic ammo box (Harbor Freight ) to protect it . Ran mine for 9 1/2 hours and it was still showing 14.1 volts on my 1242 . Also hooked to my black box . It was only 250 with a charger shipped to my home .
Some using drill batteries for each but need a adapter . They come in different amp hour ratings and also need charger unless you already have one . Also the longer distance from battery the bigger gauge wire you need or voltage drop increases .
Are you running a 9'' screen and a black box or battery on each one ? I am running a 12'' screen and black box on one battery .