Batteries??? automotive, marine, golf cart

[fishrdan]

I need to buy 4 batteries for my boat and would like to get the best battery for each application. As I understand it, marine batteries are a compromise between an automotive start battery and a deep cycle battery, they can serve both purposes. But would it be better to buy and auto battery solely for the engine and then deep cycle (well golf cart) batteries for the trolling motor, and other accessories that would be run while on the hook?

I'm considering 2- 6V golf cart batteries for my house/accessory batteries instead of paralleling 2- 12V marine batteries. Would golf cart batteries be hurt by starting the engine (140HP Mercruiser) if my start battery goes dead?

Also, is it a bad idea to use an automotive battery in a boat since it could sit for a month or 2 without being charged, discharging and hurting the battery?

I'm leaving out how the batteries are going to configured so I don't muddy the waters with questions/answers on switches, isolators, cabling, series/parallel configurations, etc, etc...

Thanks,
Dan

 

[Big Keepers]

Re: Batteries??? automotive, marine, golf cart

Marine batteries are different from auto batteries in the way they are constructed inside. The strength of the plates, the rigidity of the plastic, stuff like that. They are subjected to a lot of bouncing, jarring and rough stuff at times and regular cheap auto batteries could fail internally. Also a lot of times if you buy a marine battery from like Sears or something, the positive post will be a 5/8 size instead of a larger 3/4 size. My starting battery is a Sears Diehard and it is like that. It doesn't matter much but the positive cable lug fits loose on the post so I doubled up the lockwashers.

You can buy marine batteries that are for starting, meaning they have a lot of cranking amps but not a whole lot in the way of amp hours. Or you can buy deep cycle batteries that have a lot of amp hours but not as much cranking power. You'll see a lot of different stuff, "dual purpose, cranking, deep cycle." The important stuff is the numbers. Amp hours let you leave your electronics on, play the stereo all day, use a trolling motor and the battery will handle the drain a lot better. The thickness of the plates inside allow for a lengthy discharge.

Cranking batteries deliver a lot of cranking amps for a short period of time. The plates inside are a bit thinner so you get a faster flow of amps through them but the downside is it can lose its charge quicker. You wouldn't want to run a lot of accessory electronics all day on one because it would die quickly. The dual purpose batteries are just really strong batteries with usually about 90 or so amp hours and as many as 600-800 cold cranking amps. Forget using smaller golf cart batteries and linking them in parallel unless you are really scamming for space. Two decent deep cycle batteries will be just fine and in a pinch you have them wired so they can be combined to start the motor if one is failing.