Marine batteries and deep cycle batteries are not the same thing. Deep cycle batteries are meant to be ran down and recharged many times without causing excessive damage to the batteries. Starting {cranking}, batteries are meant for a quick, high discharge needed to start a vehicle. They are not meant for long slow discharge. Marine deep cycle batteries are really a combination of both deep cycle and starting batteries. They are not the best at either, but are a compromise as a boater needs things like fish finders and radios running when the engine is not running, yet still needs to start the boat. True deep cycle batteries are best for house batteries. Generally you will get more storage capacity out of two 6 volt deep cycle batteries than you will two 12 volt ones. These are the same type that a golf cart would use. Just thought I would put that out there, as lots of people seem to believe marine batteries are true deep cycle batteries, when in fact they are not. Cheers