I run a yello top in the front and a same amp hour in the back , i have just linked them witha cut out switch,  it does make things easier but i havant winched alot for ages so i havant properly tested it out,
I do know when the car was sat around the front battery had gone flat , just had to switch on the rear one start her up and then let it charge was well handy.
only issues was i had to get the in sync. basically let the rear go flat so it was tricked by the front one , it sems to work fine now which ever battery is low it seems to draw the charge as I have two voltmeters