I need a new cranking battery for my boat. My boat has a 25hp motor with a regular battery. Would it be better to get a deep cycle like the one for my trolling motor? Also what size of battery should I get. I run a depth finer and have my running lights on it.

I need a new cranking battery for my boat. My boat has a 25hp motor with a regular battery. Would it be better to get a deep cycle like the one for my trolling motor? Also what size of battery should I get. I run a depth finer and have my running lights on it.

Deep cycle batteries for trolling motors are designed different than batteries used for starting an OB motor.   Can you use a DC for engine starting? Yes, but it won't hold up anywhere near as long as a battery designed for the purposes of engine starting.  

Actually, for your 25, a deep cycle battery will work fine.   In larger motors, no, you don't want to use a deep cycle, it will not provide the cranking amps required for your big V-6's.

Cranking batteries are designed to deliver large amounts of amperage over a short duration and are not to be repeatadly discharged.  

Deep cycle batteries are designed to deliver much less amperage but over a much longer period and are designed to be discharge several hundred times.

Some of your large motors can draw over 100 amps during cranking, more than a deep cycle is realy designed to provide.  This causes the cranking voltage to drop, sometimes to the point that it can hard starting problems on those motors because the ignition electronics voltages drop, causing a reduced spark to plugs and injectors.

I Would go with a deep cycle. Get an Optima if you can afford it, if not I have a Duralast Starting battery from autozone and it works great.