Originally Posted by The Sailing Podcast
My question is whether the car battery might damage the starter or other systems? Any ideas? Does the CCA have to do with amps available or amps delivered?
First - there are only DC Amps and DC Volts - not car or boat or airplane or whatever. So no, using a car batter to crank a marine engine will do no damage. In fact many of us, myself included, use golf cart batteries in their boats. Usually they are used as house batteries but if you have a big house bank as many cruisers do the fact that they are not optimized for starting the engine is of little consequence.
CCA, MCA (marine cranking amps) are just specifications. They all relate to how long you can crank the engine at a particular current before the batter is exhausted. Every battery could be rated as CCA and MCA etc. It is just what process is used to rate the battery's ability to deliver current.
Of greatest importance is how much you draw down a battery. Batteries have lives calculated in charge - discharge cycles. It is generally a bad idea to discharge a battery more than 50% so usually the charge discharge "life" is based on a 50% discharge followed by a recharge cycle - lets say 1000 cycles is the life. But if you only discharge the battery 10% each time you are going to get a lot more cycles.
Cranking is also temperature senstivie. No only does the battery current and charge parameters change (not usually enough to care about) but cranking a cold engine full of thick oil takes a lot more current than a warm engine.
So, the bigger the battery the longer the life. Most batteries on casual use boats die because they have been cooked (left on the charger too long) or dry out. So a sealed no maintenance battery can be worthwhile.
1. Use your car battery (then what, push start the car down the hill and pop the clutch to jump start it?) Did that a while in my youth.
2. Bigger is better but the constraint is usually the size of the battery box. You should enclose the battery in a box so that if it leaks it can't damage the boat.
3. Most of all - fair winds and following seas.