Hydrometer readings and saving or extending battery life

Hi Paul,

First question you asked about not finding the “sick” batteries is not unusual.  I am running with Deep Cycle Marine Batteries and came across the same situation.

When you check a battery in the string, it will probably look OK – other batteries could be providing the voltage to “charge” the bad one.  Out of the string, the battery with dead cells will probably “self-discharge” in as little as 24 hours (Good batteries should hold steady).

The dead cells may have internal short.  The high heat might have caused the plates to expand and get too close together - expanded plates will probably show bulge on battery case.

Also, there could be pieces of metal that flaked off the plates causing the short. I have had some luck getting pieces out dead cells using the hydrometer to rapidly pull and push the electrolyte out of the cell. (you either see black pieces come out, or the short breaks free and settles to the bottom).

DeSulfation can sometimes restore these dying batteries. I have used electronic desulfation which “pulses” power into the battery, and basically “vibrates” the junk off the plate surfaces.  (Try searching for desulfate on this website and others). I have not tried the chemical desulfate products (maybe others on this forum can comment).

One interesting thing about batteries with dead cells is they appear to charge faster than normal. If bad batteries were in the string, they would bring overall voltage up before remaining batteries get a full charge.  The shorted cells would then begin to discharge and pull even more power out of the good batteries. (i.e. the 1250 reading)


For the second question about the whole bank, two and one-half years isn’t very long.  However, if the State of Charge (SOC) goes below 50% on a regular basis, that could shorten the life (since I don't know your system and usage, I make no assumtions).  Not too sure about the humidity…never thought about high humidity on battery life (I guess it could make venting difficult during the equalizations)

My guess is that the dying batteries were slowly draining the whole bank, and even the equalization did not give all the batteries the refresh they needed.

My suggestion: Leave the bad ones out of the string, then “run the system hard” (Heavy discharge). Let the bank fully charge once or twice and then equalize again.  I hope the hydrometer readings will slowly improve by themselves.

Hopefully, I haven’t made this reply too long.  It’s hard to explain things in short sentences.

Best of Luck with the batteries, and enjoy the Grid Free Life!

Hi Scott, thanks for the great long reply (more info is always better than not enough!).

Hmmm ok, the way this all started was my wife check the reading one morning and it was 23.8 (24V system), when usually it is 24.8 or 25. So it is very seldom that we take the bank below 50%. Anyways, the first thing I did was to check for any loose or corroded terminals (all were tight and found 2 or 3 with a small amount of corrosion). After that is when I went on to do more testing.
I am aware of DeSulfation and have had a unit in place for about to years. One question for though, I was always under the impression that having it hooked up any where on the battery bank, that it would work on all the batteries... is this correct? Also, even though the batteries in strung together, I was only having it connected to one of them (thinking that it is 12V) as I never received any paperwork with it.
One thing that I was surprised about, is you never mentioned anything about heat.

As for the batteries, each 12 are strung together, i.e. all 2 year olds and then all 2.5 year olds. But then they are connected to make one large bank. The 2 sick one were from the older side.

Thanks again for your great information.

You are sooo correct, and nothing can replace experience!
Thank you for the link, they look like a way to go on the next set of batteries.
Back to my current batteries what are your thoughts on adding a half ounce (or a full once) of acid to each low cell? This would be after trying your earlier suggestions.

Thanks again for sharing your experience.