Battery not maintaining voltage at night

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stephen-1975 asked Jan 24, '20

Battery not maintaining voltage at night

I have a set of 4 135amp led acid flooded batteries and no electric hookup for a inverter/charger. My batteries voltage seem to drop quite quick in the evening. When I test charging from the solar system and batteries from the controller all seems OK. From the alternater to the battery seems OK too. When testing the acid level shows as needs charging but when my engine is running the monitor suggests they are 14.4V

Rather than trying to get the batteries out to put them onto a 7 stage battery charger I believe there is a high output alternater with a 3 stage charging system involved. How do I find out which one I need with my current set up? Think they just need to have that good charge but they are too heavy to be lifting in and out of the battery bay every time it's needed

battery charging

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Justin Cook answered · Jan 24, 2020 at 11:42 PM

@Stephen 1975 your best bet if you're looking for a smart alternator is probably a Balmar or something along those lines; I'd suggest contacting a marine parts supply store for information.

That being said, from what you describe I don't believe you have a charging problem; your statement that "the acid level shows as needs charging" indicates that, if I'm understanding what you mean correctly, your batteries are on their way out and need to be replaced soon. The fact that they show 14.4v when charging just means that your alternator is doing its job; the problem appears to be that they're not holding their charge, which is a sure indication that they need replacement.

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JohnC answered · Jan 25, 2020 at 05:48 AM

Hi @Stephen 1975

I'd hate to see you go out and buy a new charger, or even abandon your batts straight off. All might still be well.

You don't actually say how low your Vbat goes. But pb's are very 'reactive'. They're either pushing or pulling a chemical process. Under charge they may show 14.4V. A moment later with no charge and a load applied they may show 12.0V. Same state of charge.

If you could leave them overnight to complete the chemistry, they should settle to a standing V of ~12.6V if fully charged.

I've never had much luck testing sg, perhaps because the chemical reaction takes so long to complete. Much preferred is the 'tail' current, where you compare the A they're accepting with their Ah capacity. For me, 2% is getting close, 1% would mean they're done. That's dependent on V too, but if that charge levels off they'll usually be finished.

So don't go jumping at shadows, just get to know them a little better.

You may not be able to measure A, but it's important. Not to say that every last little piece of blue kit will have it onboard, but the option of adding it is always there.

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Answer 1 · 2020-01-25T09:25:46Z

stephen-1975 answered · Jan 25, 2020 at 09:25 AM

When I got up this morning they were reading 12.05

Previously when putting these batteries on a landlines 7 stage charger it has "brought them back to life" but I haven't done that in some time as the weather hasn't been the best. I can do it one at a time but means getting in a very cramped area and trying to get the battery out.

I do believe that a 3 stage alternate would do the same but which do I buy (7 stages being de sulphering one of them and I think the 3 stages has that feature too)

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JohnC ♦ commented · Jan 25, 2020 at 10:42 AM

From your history, you have a Victron 100/50 mppt? That can do what you may want (equalizing/desulphating, etc), despite it not being advertised as an 'x stage' charger. And do all of your batts at once.

What it may lack is enough solar grunt to carry it out. If that's so, a separate 'shore power' charger could be paralleled in to help it out.

Without deeper info though, I've a sneaking suspicion that your batts simply may not be seeing enough charge each day. Eg. Starting the day at 12.05V, you could perhaps expect to need like ~3 hours in Absorb, then more in Float to finish them. Do they get that?

There are fans of equalizing, but if your batts are wired 4x in parallel, they may get out of balance in the process, and overheat one or more. A 'touch test' can find that, best stop then. This may actually be happening now in a normal day, and if so your issues may be more serious..

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