Dual Battery Question

[kodacachers]

Hi All, I'm looking for battery advice. I have a dual battery system for my boat. I need to replace one battery and am thinking of doing both just to be safe. My questions:

1. Opinions on the best batteries on the market? I don't mind paying more for peace of mind and am thinking of AGMs. I've heard Optima is great.
2. Should I get 1 cranking battery and 1 dual purpose? or 2 dual purposes? (I like the idea of having two of the same for some reason).
3. Thinking about getting a charger at the same time. Opinions? On-board or not? Float charger?

I have a 5.0 liter Mercruiser. I have standard lights, blower, etc. and a fishfinder, no electric motor or other big battery suck. I'm set up with a Blue Sea isolator, that's supposed to isolate the engine and house batteries

Thank you for your input.

[Bodofish]

As a general rule, Deep Cycles are best in boats. If you are concerned with cranking get dual purpose. I've never had anything but Deep Cycles in my boat and it has an oil pressure ignition cut out. So you have to crank till the oil pressure is up before it fires. Mine has a GM engine too.

[BARCHASER10]

I'm sure no battery expert. I have dual batteries on my Seahawk that I bought new in 2005, Yamaha OBs. My practice has been to buy Interstate marine batteries at Costco (about 80 bucks), write the date of purchase on the outside of the battery with a sharpee and replace every 4 years. I keep the boat in my garage and I always have the little black box charger/maintainers plugged in. I've never had problems, plenty of cranking power and I use Scotty electric DRs, FF, GPS , VHF, and a sound system. I coat the terminals with NAPA Terminal Protector. I have moored the boat at Everett 3 months every year without the chargers plugged in and no problems.

[Bodofish]

Yep, that's the battery I use too. I think a guy could spend a lot more but at the end of the day they're a really good bang for your buck. I used to fly paragliders with the fellow that owns the local Interstate dist., and I know for sure he stands behind the batteries 100%.

[kodacachers]

Thanks guys. I think I'm overthinking this. Costco it is.

[Larry3215]

The key is to get a good charger and use it regularly. A good AGM is going to cost you $250-$300 each. They will last a long time, but if you take care of them, the Costco batteries will last almost as long and cost a lot less over the same time span.

I would change two things from the above - use a starting battery for starting and a true deep cycle for the house battery and keep them separate unless you need to do an emergency start.

The BlueSeas isolator is good but an ACR is better. The diode type isolators actually prevent the battery from reaching full charge - which is not good over time.

[Larry3215]

Oh - by a good charger I mean a smart charger that has several stages and can maintain a battery over time.

This guy has a good rep and he sells re-manufactured chargers for a very good price and good warranty.

http://chargerguy.com/" onclick="window.open(this.href);return false;

[kodacachers]

Thanks Larry! Will order from Chargerguy!

[Sideburns]

In my opinion, agm is a must on a boat. Agm batteries normally do not gas at all, therefore dont cause corrosion issues. There are many more advantages too.... The Deka intimidator agm batteries are pretty easy to find locally, and they are "rated as" a starting and deep cycle battery. Ok quality, lower (150?) price.

Northstar and oddessy are maybe the best agm batteries ever made, but they are proud of them. I bought my first Northstars in 2005, still using them today! over 10 years, and they are deep cycle agm group 24 batteries being used (abused) as starting batteries in a diesel truck. I thought they were failing a while ago, then I tightened a loose battery cable, still going strong! Expect to pay over 300 for a northstar though.

Also, chargers... The NOCO line of chargers is fairly new, Chinese made, but seems to be good quality. They are supposedly a high frequency pulse charger/ maintainer, and claim to be able to revive batteries from the dead. Not the cheapest, but have an on board marine type, avail in multiple bank configurations. The 2 bank is called the gen2 or gen2 mini. The supplier mentioned above may carry them, and usually easy to find locally. Noco makes an isolator too, but I have no experience with it...

I have been using the same private battery distributor here in the south end for almost 15 years for my automotive business. I'm willing to help you locate stuff if needed...