Ran 2 Kinetic 2000's on a perk switch. They are 12v deep cycle audio comp batteries.Used both as starting and audio batteries. Sealed, Gel, powerful, no maintenance, lasted from 2007 til 2 months ago. New they are around $400 each, well worth it. If you do some searching, you can find them for around $300 each. I replaced both of my batteries 2 months ago because one went bad, the other was still good (but as Grant mentioned above, all your batteries should be matching). This time I decided to give a pair of slightly used/refurbished sealed gel 12v deep cycle batteries, same as the Kinetics, but were from a battery bank for a generator or solar powered system. They were 1 year old, tested as new, and were only $80 each with a 6 month warranty.
I will report back... hopefully in 7 years, that they are still working well.