Jeez, what kinda alt do Bonne'* have stock? I run a CS130d (105a advertised, apparently less) and with 1750RMS I was getting negligible drop with stock front batt, rear marine batt (just a generic g2
, 1/0 power and grounds, and big 3 in 4 gauge.
It'* nice if you run a marine batt because they use threaded posts which also make for nice distribution blocks =P
I did not use an isolator, nor would I recommend it. It'* just another failure point and more cost. I did run two fuses though; one 18" from each batt. Fuse these for the maximum current your wire is rated for AND NO MORE (my wire is rated to 350, I run 325 amp fuses because I found them locally for cheap, and by cheap I mean free.) I also recommend a fuse by the batt on your run(*) to your amp(*) rated for the amps themselves (even if they're internally fused) but that may be a touch of paranoia.
If you're like me and don't use a sealed battery you will want a battery box. If the battery leaks without a box you will get yummy corrosive acid all over your trunk and you will soon have a holey trunk floor. Also batteries can release hydrogen gas when being charged, this is toxic and super-flammable.