No DCs on Boats?

[Jonah]

Hi all,

Was just speaking with a parts rep at Pompano Beach Marine (one of largest Grady dealers in country, I believe). She tells me that deep-cycle batteries are rarely used on boats, since they can be hard on the charging systems, or even on the alternators from the outboards. She says that for house batteries, almost all Grady boats are equipped with dual-purpose batteries instead.

I find that hard to believe. Any thoughts? I'm picking between a Deka Marine Master DP27 and DC27 for my house battery. At the moment, it isn't wired to be recharged by the outboards, so until I fix that it will just be recharged by my Battery Tender Jr whenever I'm at dock.

 

[SkunkBoat]

I would get the DP27. It will work great as a house battery and still be a useful starting battery. In fact, would would use them in place of starting batteries if I needed new ones.

 

[Jonah]

Thanks Skunkboat. I just recently had to break down and buy a new 24M5 here in Nassau (at twice the price), but plan on getting a DP24 for the other starter, since it has the same CCA plus extra reserve power. The DC27 actually has the same CCA as my 24M5, so it would work fine as a backup starter too. Since my house battery is not currently re-charged by the outboards, I thought I'd go for the DC27 for the extra reserve.

Just wondering what others think about PBMC's claim that DC batteries are hard on chargers, and therefore rarely used on boats?

 

[Doc Stressor]

True deep cycle AGM batteries can tax an alternator/rectifier by accepting a very high current flow because of their low internal impedance. But this is only a problem when the battery becomes heavily discharged.

Conventional flooded cell deep cycle batteries don't have this problem. However, they self-discharge more rapidly than starting or dual purpose batteries, which is why they are not commonly used in boats except for trolling motors.

Dual purpose batteries are generally the best choice for marine outboard use. Their thicker plates hold up to pounding and vibration better than starting batteries, yet they can still deliver high cranking amperage.

 

[Jonah]

Got it. Thanks Doc. I will go with the DP27 for my house battery.