Derp cycle can be used for starting... Not preferred though as they are not designed to provide a whole slug of amps in a short period of time like a starting battery is. The CCA (or MCA) ratings don't tell you how 'fast' the battery will deliver the amps, just how much capacity the battery has. These are several different ratings that mean different things. I have a starting and deep cycle battery on my boat (F250 O/S Yamaha) and the CCA of both batteries is nearly identical, but I want each type of battery for the designated purpose. I have both batteries 'electrically' separated, but can combine if an emergency. If you have a flooded lead acid battery, take the cell caps off and look inside. The plates will be thinner and (more of them) in a starting battery vs a deep cycle. Taking a starting battery down to a deep discharge level will end up warping the plates and kill the battery. If I had a choice between having only one type of battery (like David runs) it would be deep cycles for that reason. Take it down, bring it back up, it'll last. Just my (professional) $0.02 worth...
Rick
Thanks Rick for that. What do mean by electrically separated, by those 1/2/BOTH switches? Have you ever ran into problems with either one of your batteries...Since this will be a fairly large expense, I want to do it right. I am running a Suzuki 150.