dual battery setup.

[dorourke]

I needed to replace my batteries, they were old and not chargable any more. I ran to West Marine to get one to start the engine. I bought a West Marine Sea Volt Deep Cycle 75 amps per hour. Do I need to have the same type battery for the second one, or can I get away with a cheeper and less performing one?

[nightowle]

what kind of boat do you have, and what do you usually run on electric?

[sailingdog]

If they're going to be part of a single battery bank, then you really should get two of the same batteries to reduce problems caused by different charging/discharging rates. If they're going to be separate banks, then you can get a different battery, but I would stick with the same type of battery—if you have a wet cell, get another wet cell, etc...

75 Amp-Hours is a pretty small house bank, and unless you are running your engine all the time to re-charge the batteries or don't use much in the way of electronics, you probably want to get more capacity in your house bank.

It would help if you said what kind of boat you have as well as what kind of charging capabilities you have aboard—high-capacity alternator, wind generator, solar panels, etc.

[dorourke]

OK. My boat is an S2 8.0B with an alternator and full charging capabilities. I only plan to use limited electrical, such as nav lights and radio when needed. So Sailingdog, what youre saying is if I get a lesser battery for my dual setup then the lesser battery might draw power from my better one when I use the both switch? I know the setup is in parralel. Woulden't it be like two gas tanks? The maine a higher octane with more capacity and the reserve with a lower grade as well as a smaller capacity?

[sailingdog]

What I'm saying is that the batteries in a single battery bank should be of equal size age and chemistry type. If you mix battery sizes, the smaller battery will likely be overcharged and overdrawn much of the time... leading to a vastly shortened battery life. If you mix battery chemistries, then a wet-cell may not be fully charged while an AGM in the same bank is close to fully charged, since they have different charge acceptance rates due to their different chemistries.

If you have two separate battery banks, and only combine them in an emergency, like to start the engine... they can be different size batteries. I would still recommend you use the same type/chemistry of batteries unless your charger can handle multiple voltage outputs independently—most can't.

[Ronbye]

I also have to replace my batteries and I am thinking about changing my house battery to two 6 volt golf cart batteries and keep one 12 volt starting battery. Anybody have any suggestion as to what brands are reasonably priced. My funds are limited. As well, what do you think of this setup?

[sailingdog]

Ronbye-

I have two Trojan T105 6V batteries as my house bank, but will probably add two more to make a larger house bank. It's a good way to go, and they provide a lot of power at a reasonable price. I wouldn't go cheap on the brand, since that usually ends up being a bit more expensive in the long run.

[dorourke]

Sailingdog, although my head is spinning, I do understand what your saying about the draw factor and such. It's probably better to have the same two batteries. What is the advantage of a six volt over a twelve volt system?

[sailingdog]

cost and size. Two T105 6VDC golf cart batteries give you a fairly decent small house bank of 210 Amp-hours when run in series for a fairly low price.

[dorourke]

Originally Posted by sailingdog

cost and size. Two T105 6VDC golf cart batteries give you a fairly decent small house bank of 210 Amp-hours when run in series for a fairly low price.

So there would be no need for a dual batterie switch? I would just need an on or of switch? What if one batterie fails? woulden't that leave me without backup?