Hi pNuker,
Go to Napa and get a perko switch--rated at 100 amps--1000 amps contacting.

pNuker wrote:
I'm also looking for a method to divert the charge from the isolator to my extra backup battery (damaged agm battery discussed over here) when it needs. I was thinking about getting one of those marine battery switchers to manually switch to it when my main cabin batteries are already charged up. Something like this:
http://www.amazon.com/gp/product/B000K2MCR2/ref=ox_sc_act_image_1?ie=UTF8&smid=A1UNWS4MSNTF2A
It looks like the perfect switch dual rectifier would accomplish this, but like I said it's way too pricey...