Brand aside what am I looking for in a deep cycle battery? As far as AMPS etc. Ive seen them price from 90 bucks up to 300 bucks. Also I have two batteries now one for each engine. Thinking about a stereo. If I were to add a third battery how do you hook that up so its stand alone but can also be charged during running.

I have never been a fan of deep cycle batteries for big boat engines.......You kind of want to look for heavy duty starting batteries and put the biggest battery that will fit into your battery boxes. Something like 29 series batteries with dual terminals so you can hook up any other equip. directly to the battery .The new AGM batteries are really great but their a little on the high side in price ..batteries are not the items you want to cheap out!!!Good luck


Jim

thanks yeah I hear ya. But I think I would at least want to keep one deep cycle at min just for the reliability

Deep Cycles are good to use as a stereo battery. They are made to run up and down, where standard starting batteries are not.There are several ways to hook a third battery. You can run it through a battery switch or and isolator. It depends on what you have and how you want it to charge(automatically or manually).
You can get decent wet cell deep cycle for about $130 or an AGM will run about twice that much.

Using a third battery (deep cycle) for long power draw applications is an excellent idea. You would have to engine batteries for starting and a house battery for accessories. You could use a VSR to maintain the house battery charge. A VSR is a better replacement for an isolator. VSR Voltage Sensitive Relay is much more reliable that isolator technology. What happens is the relay closes the circuit (connects the battery to the charging system) when voltage reaches a preset threshold like 13.7 volts. It opens the circuit when the voltage drops bellow 12.3 to keep from draining the engine batteries.