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Old 10-26-2017, 06:16 PM   #1
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Mixing old and new batteries

It is time to replace the Odyssey 2150 AGM batteries that make up the house bank. They are slowly going down hill but I believe they would still work fine as starting and thruster batteries. At least for a couple of years.

I understand that mixing old and new batteries in a single bank is a bad idea.

Question: is there any reason why I shouldn't point my chargers at the house bank (new Osyssey AGM's) and use ACR's to charge the older start and thruster banks?

Note that I have more than enough charging capacity for this setup.

Thanks!

Arch
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Old 10-26-2017, 08:22 PM   #2
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I'm no expert on such matters, but it seems like a reasonable plan to me. Particularly if you were to turn the ACR's off when not charging. This is what I do, but my house and start batteries are all of the same age and type (Odyssey PC 1800)
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Old 10-26-2017, 08:27 PM   #3
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I have recently installed 3 x 2150's in the bow as thruster/windlass bank. At the same time I installed a battery monitor. I see that neither the windlass or the truster use very many Ah per run, so I believe less capacity would have been OK.
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Old 10-26-2017, 10:39 PM   #4
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ACR - automatic charging relay- is nothing more than a combiner. By combining old batteries with new you won’t be charging all your batteries equally. Is this really bad, no. Is this optimal, no. Will you shorten the life of your new batteries,yes,. Meaningfully, hard to say, probably not but possibly.
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Old 10-27-2017, 07:32 AM   #5
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While I am not a battery expert, putting an echo charger between the new bank and the old one should be a suitable solution.

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Old 10-27-2017, 07:42 AM   #6
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Quote:
Originally Posted by Arch View Post
It is time to replace the Odyssey 2150 AGM batteries that make up the house bank. They are slowly going down hill but I believe they would still work fine as starting and thruster batteries. At least for a couple of years.

Slightly tangential... and only FWIW...

We've gotten excellent service from our two dual-purpose banks of 3x Odyssey PC-2150 12V AGMs.

That said, I recently replaced the oldest bank with 4x Lifeline GPL-4CT 6V AGMs, since I discovered I could cram those into almost the same footprint as the 3x G31s. The effect is to have increased capacity from 300Ah/bank to 440Ah for that bank.

Another possibility that seems to be emerging is using Firefly Oasis Carbon Foam G31 AGMs. They don't offer the same huge number of cranking amps as the Odysseys. OTOH, apparently they do seem to be living up to claims about being able to be routinely drawn down to 80% DOD without damage. They cost (another) arm and a leg and apparently there are some supply issues, but perhaps more useful for house loads.

But if you have any capacity issues, you might look into those kinds of options...

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