Battery questions

dlochner · May 4, 2020

Fred, yes the GC batteries are better at deep cycling. With 2 batteries you would wire them in series. The charger will see them as 1 12v battery so nothing special will be needed.

When wiring in series, the amp hour capacity remains the same, the voltage increases. So, a 200 amp hour 6v battery wired in series will give you 200 amp hours at 12v. Wired in parallel, the same batteries will give you 400 amp hours at 6 v.

Golf cart batteries are designed to be deeply discharged every day. They are more robust than "marine deep cycle batteries." They are also cheaper, because, well there is larger market for golf carts batteries than marine batteries.

If you don't have refrigeration or other high energy demands, one bank of 2 GC batteries will be fine.

Check out the Musing With Maine Sail forum here and on his website (MarineHowTo.com) for more info on deep cycle batteries.

Davidasailor26 · May 4, 2020

Generally speaking golf cart batteries are considered better for deep cycling applications than normal group 27 or 31 12V batteries. Though it may vary based on manufacturer. Look up Maine Sail’s posts on that subject.

You can add the amp hours, but do take care to convert to 12V first. For example a 6V golf cart battery that has 220 amp hours is giving that rating at 6V. At 12V that’s only 110 amp hours. So two of them in series would be 12 volts, 220 amp hours.

Battery chargers charge based on battery chemistry, so as long as the charger can be set to match the chemistry (e.g. flooded lead acid, AGM, etc) it should work fine. Just hook up the charger to the “outside” of the serial pair so it’s charging both batteries at once, same as the load.

BarryL · May 4, 2020

Hey,

You can use 6V golf cart batteries. You do need to wire them in series to get 12V. The amp hours are NOT added. you need two batteries to get to 12V so the AH stays the same as for 1 battery. For example, if you use a Trojan T105 6V battery, and each battery has a 200AH rating then the two batteries together will have 200AH (at 12V).

Are they 'better' than 12V deep cycle? That's a more difficult question. There are 12V deep cycle batteries that are better than 6V GC , and 12V Deep cycles that are worse. What is your goal? Do you want more capacity, lighter weight, lower cost or ??

Regarding your charger, you need to make sure that it can work with the battery type you buy. For example, are you buying flooded lead acid or AGM? That determines if your charger will work or not.

Good luck,
Barry

capta · May 4, 2020

If you have the footprint for T-105 batteries you would be much off with T-145 batteries. They are much better batteries for marine use, just slightly taller.

dlochner · May 4, 2020

Trojan batteries have a well deserved reputation for quality and longevity, however, the cost/benefit for Fred's boat might be a little steep. He has a Grampian 26, I believe with an outboard.

capta · May 4, 2020

dlochner said:
Trojan batteries have a well deserved reputation for quality and longevity, however, the cost/benefit for Fred's boat might be a little steep. He has a Grampian 26, I believe with an outboard.

Alrighty then. Perhaps T-145s a bit of overkill.

Benny17441 · May 4, 2020

As far as which batteries are best, you have to compare apples to apples. Cheap Golf Cart Batteries will usually be a little better than cheap 12V deep cycle batteries. The plates made of a lead alloy are usually heavier and yield more charge/discharge cycles. The usual comparison is between 2 (6V) and 2 (12V) as these combinations will yield approximately the same Amps. In weight and size the 6V will be a little heavier and larger. The major drawback for 6V is that if you loose one of the batteries you loose total 12V capabilities while with 2-12Vs you just disconnect the bad battery and continue on the other. To counteract this many have a 12V engine starter independent of the house bank or go for 4 6V batteries if they have a need for a larger bank. A larger bank may require a larger alternator and an upgraded inboard charger.

Ron20324 · May 4, 2020

Looks like he has an outboard. I hope he can charge all that lead.