a higher amp alt would do a better job of keeping both batteries "full". I'm not sure what the factory alt is rated at, but, personally, I would go w/ 100 amps minimum.There are bigger ones available, up to 160amps..maybe a bit overkill unless you do some onboard welding, lots o' winching, and bbq a squirrel
on occasion!. Determin what electrical items you are currently running, and what items you may add in the future.I am using a GM CS130 100 amp alt (stock one was rated@ 40 amps), and it runs the stereo, compressor, aux lights w/ no problem..check out "alternatorparts.com" for upgrades avail for this particular alt.Hope this helps.
