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Old 04-07-2020, 07:42   #1
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Second Battery advice

I just bought my first sailboat, a Sabre 28. It normally has two batteries, currently it has a single WEST MARINE–Flooded Marine Starting Battery, 650MCA, Group 24 battery. Do I have to use the exact same type or can I get a non flooded non lithium one?
Also, interesting when the battery select is Off and I switch the DC panel breaker on, the lights work. Is that normal?

Thanks.
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Old 04-07-2020, 07:49   #2
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Re: Second Battery advice

Two batteries need to be the same type, as in flooded or AGM. They charge differently and can mess each other up. Past threads have recommended the Duracell series for those of us not going high tech, with Sam's Club having good prices. Your lights apparently skip the rotary switch. No. Everything but the bilge pump(s) should be on the switch.

Separating the two, so that you use one for house and one for starting, is a bit of valuable redundancy - if one fails, you can parallel them or use the other. Ordinary jumper cables are another way to avoid OS moments.

Congrats on the boat.
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Old 04-07-2020, 08:11   #3
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Re: Second Battery advice

Congratulations on your new boat. Many years ago I owned a Sabre 30 and remember her so fondly.

A starting battery is - as the name suggests - meant only for engine starting. It will be quickly ruined if repeatedly discharged to say 50% as you might when anchored out for the night.

What you want is a “deep cycle” battery. My old Sabre was set up so the you ran off one battery using the selector switch. Each day I would switch batteries (they were both deep cycle). Never leave the selector switch on “all” - someday you’ll forget and run down both batteries and not be able to start.

So I would do one if the following

1) get a deep cycle battery (not an AGM which don’t last long either in deep cycle use) Always leave the selector set to that battery (except maybe one day a month to keep the other battery charged). If you ever can’t start your engine because the deep cycle “house” is too discharged, switch to the start battery. If you go this route consider getting a bigger than group 24 battery. A group 27 or even 31 will let you enjoy anchoring out over night much more. Of course you need room and a suitable battery box.

2) get rid of the start battery and buy two deep cycle. This was likely how it came from Sabre. Batteries only last about five years so your current battery may be near the end of its life anyways.

3) with the help of an electrician or knowledgeable friend rewire the boat to take out the selector switch. The start battery then only starts the engine. A new deep cycle house battery does everything else. This arrangement usually has a “parallel” relay to momentarily connect both batteries together if the start battery is dead to get the engine started.

And you are right that you should not be able to turn anything on when the battery switch is set to “off” (except the bilge pump). Something is wired wrong.

Here’s a long but excellent discussion by MaineSail https://marinehowto.com/1-2-both-bat...onsiderations/
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Old 04-07-2020, 08:33   #4
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Re: Second Battery advice

You can combine batteries, no problem. You should likely have at least one deep cycle battery if your switching separates the batteries like they often do. The above posts are however correct; it's BEST to have the same battery, but not a necessity. I have had many combinations of batteries including a Gel and flooded bank on one boat. It the end, it made no apparent difference. For your second battery get the biggest that will fit in the tray of box. Group 24 is not a very big battery.
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Old 04-07-2020, 09:35   #5
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Re: Second Battery advice

I’d highly recommend a west marine AGM, it’s a sealed system, it won’t leak and they have a 1yr zero questions warranty, on my system I have a group 31 for battery 1/start, and a lithium for battery 2/house, if/when I add another battery it’ll be a second lithium running beside by existing house battery.
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Old 04-07-2020, 10:41   #6
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Re: Second Battery advice

There are some good ideas above, but the charging circuit has been left out of the conversation. I've been taught (by the forum electrical experts!) that different types of batteries have different charging cycles, and my battery charger certainly wants to know what it is sending the amps to. How are these two batteries charged? One charger to both from shore power? I think they should be of similar type. Alternator on engine for one, shore charger for the other? Then are they separated for charging? Combining them at the rotary switch is as good as paralleling them.

I don't know all the ins and outs for this, but I don't think that we should leave the original poster with advice to purchase two batteries, different because one will the starting and the other house, without considering how he/she is charging them.
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Old 04-07-2020, 10:58   #7
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Re: Second Battery advice

What about putting the AC charger and the alternator on battery one, and using this to charge battery 2



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Old 04-07-2020, 15:19   #8
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Re: Second Battery advice

I forgot to mention, boat has DC only. I plan on installing AC asap so we can have shore power.
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