Deep cycle and dual purpose in same bank

[hd002e]

Battery question: i have combined marine dual purpose and marine deep cycle batteries (both are traditional, not AGM or lithium) in the same bank without an isolater in between. Will it be OK or will I see a discharge between the two?


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[btrayfors]

Originally Posted by hd002e

Battery question: i have combined marine dual purpose and marine deep cycle batteries (both are traditional, not AGM or lithium) in the same bank without an isolater in between. Will it be OK or will I see a discharge between the two?


Sent from my iPhone using Cruisers Sailing Forum

I have a feeling that you already know or suspect the answer.

What will happen depends on a host of factors, inter alia:

• age, chemistry, and condition of batteries
• how they've been used in the past (rate and depth of discharge, charging voltages, temperatures, how often they've been 100% recharged, equalization cycles performed, etc., etc.)
• how they'll be used in the future (rate and depth of discharge, charging voltages, temperatures, how often they'll been 100% recharged, equalization cycles performed, etc., etc.)
• scheme of paralleling, and size & condition of cables and lugs
• how you use your boat and what level of original capacity do you consider "good" or "need replacement"

Bottom line: You've already combined them. Monitor them as you go along. You may get the service life and quality you expect. If not, replace battery bank with new batteries of the identical size and type.


Bill

[hd002e]

Hey btrayfors,

Very valid points. I have brand new batteries though, just started combining them today and haven't put any load on it yet.


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[btrayfors]

Originally Posted by hd002e

Hey btrayfors,

Very valid points. I have brand new batteries though, just started combining them today and haven't put any load on it yet.


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OK, if they're brand new then buy additional marine deep cycle battery or batteries of the identical type to add to the house bank, and use the "dual-purpose" battery for starting or reserve or something else.

Bill

[wayne.b]

Originally Posted by hd002e

Battery question: i have combined marine dual purpose and marine deep cycle batteries (both are traditional, not AGM or lithium) in the same bank without an isolater in between. Will it be OK or will I see a discharge between the two?

===

In my experience so called dual purpose batteries are a compromise that don't do either one very well. You will end up deep cycling your engine starting batteries which will noticeably shorten their life and possibly leave you in an awkward situation someday. My recommendation would be to use AGM batteries for engine starting, conventional deep cycle batteries for your house bank, and some sort of switch, either manual or voltage sensing to combine them for charging only.

[nigelmercier]

I wouldn't even mix different brands, let alone types.

[monte]

Our cat came with 4 exide duel 160Ah lead acid batteries. We couldn't source the same batteries so added 2 similar standard 160Ah lead acid batteries. So far so good after a couple of years constant use. My basic understanding is the dual just have thicker plates. The exide also have quite high charge point recommendations and different SOC % to most batteries I've used before. They are all used for the house bank, wired together without isolation.

[skipmac]

Originally Posted by wayne.b

===

In my experience so called dual purpose batteries are a compromise that don't do either one very well. You will end up deep cycling your engine starting batteries which will noticeably shorten their life and possibly leave you in an awkward situation someday. My recommendation would be to use AGM batteries for engine starting, conventional deep cycle batteries for your house bank, and some sort of switch, either manual or voltage sensing to combine them for charging only.

Curious to know why you recommend AGMs for starting batteries? My understanding is the main advantages for AGMs are the ability to take higher charge rates and ability to mount the batteries other than flat and level. What's the advantage for starting?

[wayne.b]

Originally Posted by skipmac

Curious to know why you recommend AGMs for starting batteries? My understanding is the main advantages for AGMs are the ability to take higher charge rates and ability to mount the batteries other than flat and level. What's the advantage for starting?

===

AGMs have higher cranking power than an equivalent sized flooded lead acid battery. Just as they have a higher charge acceptance rate, they can also supply more amps for short periods of time when discharging. You can see it in the numbers when you look at CCA ratings (Cold Cranking Amps). That may not be a benefit for small easily cranked engines but in my case I'm starting large diesels and the difference is very noticeable.

[mitiempo]

Originally Posted by hd002e

Battery question: i have combined marine dual purpose and marine deep cycle batteries (both are traditional, not AGM or lithium) in the same bank without an isolater in between. Will it be OK or will I see a discharge between the two?

If they are all 12 volt batteries none are true deep cycle anyway. I don't think it is much of an issue.

Now if some are 6 volt deep cycle I would separate them.

[Terra Nova]

Originally Posted by hd002e

...i have combined marine dual purpose and marine deep cycle batteries (both are traditional, not AGM or lithium) in the same bank...

Very foolish move.

[S/V Alchemy]

Originally Posted by btrayfors

OK, if they're brand new then buy additional marine deep cycle battery or batteries of the identical type to add to the house bank, and use the "dual-purpose" battery for starting or reserve or something else.

Bill

This. My favoured combo is traditional flooded 6VDC in series-parallel, with all charging sources going to that house bank. The house bank in turn supplies via echo chargers or ACRs the 12 VDC start battery and the 12 VDC windlass battery at float voltages to basically ensure that you've got them pretty close to topped-up all the time.

As a belts-and-suspenders approach, you can provide switching to take the house bank out of the circuit and use the start as a house bank in emergencies or for maintenance. You may have to change your MPPT or other charge controller settings, but it's supposed to be a Plan B if something takes down your house bank.

This is all predicated on the house bank being comprised of identical individiual batteries that are never, or close to never, treated as other than one big battery. Mix and match brings the whole bank down to its weakest component.

[skipmac]

Originally Posted by wayne.b

===

AGMs have higher cranking power than an equivalent sized flooded lead acid battery. Just as they have a higher charge acceptance rate, they can also supply more amps for short periods of time when discharging. You can see it in the numbers when you look at CCA ratings (Cold Cranking Amps). That may not be a benefit for small easily cranked engines but in my case I'm starting large diesels and the difference is very noticeable.

That makes sense. Amps that go in fast will also come out fast.

[Dougtiff]

Your charging system should go to your STARTING batt. first then combine to the HOUSE bank [Nigel Calder].Use your DUAL purpose batt. for STARTING and the others for HOUSE bank, that way you can have different batts. this way the START is allways charged and also wire in a ON/OFF switch between the start and house bank, thatway you can combine if needed.

[hellosailor]

In theory a "dual purpose" battery has a medium-thickness plate, as opposed to the thicker plate of a true deep cycle, or the thinner plate of an SLI. The thicker plate should allow for a deeper charge cycle (which moves more metal off the plate) while maintaining the integrity of the plate. So when combined with a "dual purpose", you literally are physically putting great wear, proportionately, on the dual purpose battery and that "should" result in shortening its life faster than the deep cycle battery.
Result? Two uneven batteries and that should help to wear them both out too early.


At least, that's my understanding of it.


If they are both new...why get and mix two different battery types?? Last two left on the shelf?