MrsDigger

Can anyone provide information about the alleged issue with using deep cycle batteries in conjunction with Mercruiser engines?

hillbilly24

deep cylce batteries are designed to export relativley small amounts of current for an extended period, and take a charge back after being killed. Cranking batteries are designed to export large amounts of current in short bursts. Say you have a five gallon bucket with no lid on it, you could empty that bucket pretty quick, and refill it pretty quick, that is a cranking battery. Now say you put a lid with a pour spout on that same bucket, it would take alot longer to empty and fill, that is a deep cycle or house battery. Further compounding the problem is that deep cycle batteries sulfate quickly when you put large draws on them such as that of a starter. Merc requires a certain CCA # for their EFI engines, I think it's 750 for most of em. Deep cycle batteries and most batteries that you will find at an auto parts store don't meet this spec. The problem you could encounter is that during cranking the battery con't export enough current to run the starter and the ECM and you may have hard starting problems as well as runnability issues after a while when the plates have sulfated and can't export much current at all. Hope this made sense

MrsDigger

Thanks...it sort of made sense. I've gotten a lot of different answers to this question on a couple different websites, but nobody seems to know about the specific warning that was supposedly issued by Mercruiser. I couldn't find anything at all about it on the Mercury Marine website. My husband has deep cycle batteries in the boat now, and I'm leaning toward replacing them with the same thing, but Heaven knows, a girl doesn't want to screw up her husband's boat while he's away!

Steve Zuckerman

Hi Guys:
As an old bass boater who's ALWAYS looking for the answer to battery longevity, I recommend dual cycle batteries. They hold up better than cranking batteries, and seem to run all our 12V electrical toys (lights, stereo, fans, TV, vibrator) JUST KIDDING ON THE VIBRATOR ................
Anyway, I also added an onboard dual battery charger. That makes keeping the batteries charged and ready to rock real easy. It also works well for "shore power" when I'm overnighting at a marina. Then my wife can run her vibe, er fans all night long.
Regards,
Steve

Liberator21

Here's some interesting battery info:
http://www.wind-sun.com/Batteries/Battery_FAQ.htm
Dual purpose batteries are ok, but if you've got a dual battery system, use a starting battery for the engine, and a deep cycle for the house battery. Using that with a good quality battery combiner should work well.
One of the old West Marine catalogs had a good diagram in it for hooking up dual batteries with a combiner.

Paul

mwdill

that was on ship-shape tv last week, very informative.

dykstra

great info