Replacing all batteries in a cruising sailboat

[Mhorowitz]

I have a CAL 39 and my house batteries are 8 years old and died at the end of my last cruising season. I am going to replace them. Have been using 3 x Deka Grp 31 AGM for house bank. Also have a wet cell grp 24 for a main engine starting battery and anothe grp 24 to start the genset. In addition to the alternator and the 110 v shore power charger, I have 350 watts of Solar power wired through a charge controller to the house bank.
With all the power in the house bank nearly 3000 mca I virtually never use the starting battery.

My thought is to get 4 grp 31 Dekas as a house/starting bank. 1 marine starting batt for the genset. I could either put the 4 th Deka on the #2 bank position of the batt switch, or wire it directly into the house bank, although it is a couple of feet away, maybe 4 ft of wire path. If I wire it directly into the house bank
, I could put the genset battery on bank 2 position of the batt switch and have a way to give it a charge other than when the genset gets used. Right now the genset batt is isolated and gets no charge except when it is running

So my question is does this make sense should the 4th AGM be a separate bank or wired directly?

Thoughts appreciated


Mark

[Stu Jackson]

Sounds like a good way to increase your house bank size with the same amount of lead. Good idea. Could you use the reserve bank to start either the gen set or the engine with another simple switch?

[btrayfors]

Wiring the genset start battery to position 2 on your (presumably) 1-2-ALL-OFF switch seems the better alternative IMHO.

Wire all four group 31 AGMs together as a single bank.

BTW, I'd be willing to bet that the exceptional longevity your're getting from the AGMs is a direct result of your 350 watts of solar, with a good controller.

Bill

[Mhorowitz]

Originally Posted by btrayfors

Wiring the genset start battery to position 2 on your (presumably) 1-2-ALL-OFF switch seems the better alternative IMHO.

Wire all four group 31 AGMs together as a single bank.

BTW, I'd be willing to bet that the exceptional longevity your're getting from the AGMs is a direct result of your 350 watts of solar, with a good controller.

Bill

Bill I agree the solar really helps but it just did not make sense to me to have a grp 24 starting battery sitting there that I never used as opposed to increasing the storage capacity and night time running capacity for house use

[Stumble]

Originally Posted by btrayfors

Wiring the genset start battery to position 2 on your (presumably) 1-2-ALL-OFF switch seems the better alternative IMHO.

Wire all four group 31 AGMs together as a single bank.

BTW, I'd be willing to bet that the exceptional longevity your're getting from the AGMs is a direct result of your 350 watts of solar, with a good controller.

Bill

Best idea I have heard in a long time.

Battery bank size is directly related to the lifespan, with a larger bank lasting longer. I have never understood the idea of having two house banks.

[hellosailor]

"it just did not make sense to me to have a grp 24 starting battery sitting there that I never used as opposed to"
The purpose of a dedicated and isolated starting battery, is to ensure that it will be there and be fully charged when the house bank has been accidentally depleted or failed from mechanical reasons.

So having a small isolated SLI battery on the genset is not a total waste. If your main bank goes out for any reason, that "wasted" battery will still be there, ready to start the genset for you.

[Mhorowitz]

My point being I currently have a dedicated starting battery on the Engine seldom used but can be charged by engine, solar or AC charger if the battery switch is set to 2 or all. Then I have a dedicate start battery on the genset which can only be charged by running the genset. Also I have a house bank of +\- 270 Rc mins

How about if I replace one of the two start batteries with more RC mins.

If the remaining battery can be charged by any of the chg sources, engine, solar and AC charger and can be switched in with the batt switch to start either the engine or genset, where is my downside?

[ranger58sb]

Originally Posted by Mhorowitz

My thought is to get 4 grp 31 Dekas as a house/starting bank. 1 marine starting batt for the genset.

Thoughts appreciated

You might consider 4x 6V golf cart batteries instead of 4x G31s. That'd be approx. 450 Ah versus 400 but more importantly (as I understand it), the GCs are designed/built for better deep cycling compared to the dual-purpose G31s... and you'd still have way more CCAs/MCAs than you need to start anything.

-Chris

[Mhorowitz]

Chris

Have considered this alternative. Worry about having to monitor and refresh wet cells vs sealed agm

[wingless]

Here is a reply showing links / specifications for various Group 31 AGM batteries.

For my usage the important specification is the Ampere-hour (Ah) capacity, so I picked the Lifeline GPL-31XT, the only one w/ ~25% more at 125 Ah.

The method to increase Ampere-hour capacity is to gang multiple batteries in parallel.

On my boat I have six of the Lifeline GPL-31XT batteries to extend my run time.

[Mhorowitz]

One addition or change to your chart regarding Grp 31 AGM batteries. You can buy the Deka battery from Sam's Club for 179 ea. I have verified that they are the same battery relabeled as Duracell for sale by Sam's club. You are correct that the Lifelines give more amp/hrs per unit. But the Sam's give more amp/hrs per $. These are only on clubs east of Mississippi. West US uses a diff OEM JCI. Haven't looked at the cost/capacity info on them.

Mark

[ranger58sb]

Originally Posted by Mhorowitz

Chris

Have considered this alternative. Worry about having to monitor and refresh wet cells vs sealed agm

Well, if it's an option you might prefer, AGM GCs are available. Lifeline, for instance...

-Chris