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Old 10-31-2013
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Uneven Water Loss in Batteries

Hi All,

Strange questions. I keep my 343 on a battery charger (3 stage marine rated) while she's at dock. I also do monthly battery maintenance, including topping off the banks w/distilled H20 once a month.

In my most recent maintenance cycle, I noticed an oddity. My house bank is two Group 27 batteries wired in parallel. They are in battery boxes below the aft bunk which has a vent. In topping off the fluids, I noticed that 1 battery had much lower water level than the other. The other battery had water level that was full (required nothing) while the other was really low (almost to the point of showing the plates).

What could be causing this uneven water loss?
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Old 10-31-2013
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Re: Uneven Water Loss in Batteries

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Originally Posted by night0wl View Post
Hi All,

Strange questions. I keep my 343 on a battery charger (3 stage marine rated) while she's at dock. I also do monthly battery maintenance, including topping off the banks w/distilled H20 once a month.

In my most recent maintenance cycle, I noticed an oddity. My house bank is two Group 27 batteries wired in parallel. They are in battery boxes below the aft bunk which has a vent. In topping off the fluids, I noticed that 1 battery had much lower water level than the other. The other battery had water level that was full (required nothing) while the other was really low (almost to the point of showing the plates).

What could be causing this uneven water loss?
Old batteries develop internal shorts that generate a fair amount of heat and cook-off electrolyte. Try reversing the order of the batteries and doing an equalization cycle. That may give you a bit more time but it may simply be time to replace the batteries. I now rotate the order of our batteries about once every 6 months which, supposedly, will give them a somewhat longer life span.
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Re: Uneven Water Loss in Batteries

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Originally Posted by svHyLyte View Post
Old batteries develop internal shorts that generate a fair amount of heat and cook-off electrolyte. Try reversing the order of the batteries and doing an equalization cycle. That may give you a bit more time but it may simply be time to replace the batteries. I now rotate the order of our batteries about once every 6 months which, supposedly, will give them a somewhat longer life span.
The batteries are brand new...4 months old to be exact.

I will, however, rotate them next month if the fluid is low again and see what is going on.
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Old 11-01-2013
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Re: Uneven Water Loss in Batteries

How are the 2 house bank batteries wired? Are you drawing across them evenly or are both connections to loads only on one battery?

On a bank of 2 batteries in parallel the positive lead should come from one battery and the negative lead from the other. If both cables are on the same battery the batteries are not being evenly used.
chucklesR, svHyLyte and Seaduction like this.
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Old 11-01-2013
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Re: Uneven Water Loss in Batteries

Off gassing (water loss) primarily occurs during charging. Water loss is also higher when electrolyte temperatures are hotter.

If you have watered the batteries each month and this is the first month the water inventory in the batteries has been noticeably different (and the first that month there has been appreciable water loss) I would check to see if there is current leakage through a ground path or an overlooked load that has been draining the batteries…either of which could cause increased charging and thus greater water loss. Of course check all connections on the charging path for both batteries. Is one battery wired for starting only and the other for house loads?
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Re: Uneven Water Loss in Batteries

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Originally Posted by mitiempo View Post
How are the 2 house bank batteries wired? Are you drawing across them evenly or are both connections to loads only on one battery?

On a bank of 2 batteries in parallel the positive lead should come from one battery and the negative lead from the other. If both cables are on the same battery the batteries are not being evenly used.

This is indeed how they are wired (positive on one end of the bank, negative on the other end of the bank)
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Old 11-01-2013
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Re: Uneven Water Loss in Batteries

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Originally Posted by night0wl View Post
This is indeed how they are wired (positive on one end of the bank, negative on the other end of the bank)
Equalize them and check again after a month. You may have one going bad.
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Old 11-01-2013
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Re: Uneven Water Loss in Batteries

Would it not be prudent to do a hydrometer test on each cell to see if you have a bad cell going? You say you top off batts each month? Was led ever exposed to the air? The only time I have had to add water is when batts are going bad, excessive charging, charger never stops charging because batts never reach full charge. I have not had to add water once this year, two year old batts, but I did not use much batts this year, no long trips.

Am I all wet with the hydrometer test? viscosity testing of a battery?
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Re: Uneven Water Loss in Batteries

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Originally Posted by Delta-T View Post
Would it not be prudent to do a hydrometer test on each cell to see if you have a bad cell going? You say you top off batts each month? Was led ever exposed to the air? The only time I have had to add water is when batts are going bad, excessive charging, charger never stops charging because batts never reach full charge. I have not had to add water once this year, two year old batts, but I did not use much batts this year, no long trips.

Am I all wet with the hydrometer test? viscosity testing of a battery?
i'll do a hydrometer check, but being 4 months old, I suspect they're good. In Florida, you have to top off fluid more often. The summer temps are really harsh on batteries.
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Re: Uneven Water Loss in Batteries

A specific gravity test (hydrometer) is a good way to test a lead-acid storage battery. A fully charged battery will have a specific gravity around 1.260. Hopefully the difference between cells is no greater than .05. (The specific gravity of water is 1.0) A hydrometer reading below 1.225 shows a discharged battery or maybe a sulfated battery. A sulfated battery will not take a full charge because the sulfuric acid has hardened on the plates (lead sulfate) like dry peanut butter on a knife. A sulfated battery may have a high voltage reading but it's only a trick. Don't believe it. As a battery charges the sulfate (sulfuric acid) comes out of the plates increasing the specific gravity of the electrolyte. Hydrogen is released during charging hence the need to add water. I'd guess hot Florida weather cause evaporation beyond what we see in more temperate climes.

Another twist is plate grid material which changes required charging voltages.

A load test is a better test, but requires test equipment beyond what most people have in their tool pouch.

Specific Gravity of Battery Electrolyte - Engineers Edge

- CH
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