Third Battery - VHF/UHF Radio Install

[springrnco]

I recently purchased a Yaesu FT-8800 radio that i would like to install in my 03 H1 SoftTop. The radio has the ability to act as a repeater but my concern is that if left on(which I need it to be) it will obviously drain the batteries. First question is has anyone installed a third battery? If so where? Will an H1 start on one battery? If so could I just install an isolator on one of the batteries? Any advice or experience would be great. Thank you.