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Uneven Water Loss in Batteries

5K views 21 replies 10 participants last post by  mitiempo 
#1 ·
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?
 
#2 ·
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.
 
#4 ·
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.
 
#6 ·
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)
 
#5 ·
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?
 
#8 · (Edited)
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?
 
#10 ·
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
 
#11 ·
You can not assume that new batteries are good. And your charger could be faulty and overcharging. Or as mentioned before, you have something constantly drain that battery. You said you have two 12v batts in series? 24V system?
 
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#14 · (Edited)
Parallel is no good. Will not charge or discharge evenly. No matter how you have the wire connected.
Please give us the details & scientific dissertation on this claim. Please keep in mind that there are millions of batteries out there wired in parallel, it is one method of building capacity. This is done not only in marine applications but in industry, fire and EMS service vehicles, uninterrupted power supply systems, cordless power tools, solar, military etc. etc. on and on. Even some of the large truck makers have moved away from 4D and 8D's for engine starting and are now wiring TPPL AGM batteries, often group 31's in parallel. I have some parallel banks out there at 13 years of age still performing well. I also own the equipment to test batteries via internal resistance and well wired parallel banks survive and charge perfectly fine. If they are "single end wired" I do see imbalance issues and my test equipment shows me this is possible. When end to end wired I don't see imbalance issues any more so that with 6V batteries... I generally prefer 6V or 2V batteries but even with 6V you will need to wire series parallel to gain Ah capacity. I have some vesels I work on with banks in excess of 1200Ah. You don't get there on a boat, with the space constraints, without using parallel wiring..

Sure it would be nice if we all used 2V cells in series but they are huge, expensive and tough to fit. They represent about 2% of the banks I see on boats. When you jump up to 6V you lose many of the benefits you'd gain by using 2V cells. No longer can you measure individual cell voltages as you can with a 2V bank because the individual cells are not accessible for voltage measurements..

You need to add a combiner for even charging, but will not help with uneven discharge... MASTERVOLT Battery Mate IG 1602, 2 Battery Isolator at West Marine

Simpler to have two 6v batts in series to make the 12V and have added amps. No charging or discharging issues.
That is not a combiner it is an isolator. Again please explain for us scientifically why you "need" a combiner to charge evenly.

I suspect the OP simply got a bad battery, it happens. Another possibility is these are private labeled "battery distributor" batteries where they slap labels on anything that comes through the door. I had a customer two years ago with identical labeled/stickered batteries yet the batteries were completely different brands and not even a similar case.. Differnt brands use water at differnt rates. Also the battery losing water could be the battery closest to the engine and running at a higher temp. I have even seen batteries get heated by dark colored topsides when the sun comes up. The SG should be checked to confirm there is not a cell going bad...
 
#16 ·
I agree with Maine. Parallel works well in installations on boats as in industry. I have installed 12 volt batteries in parallel as well as 6 volt batteries in series/parallel without issues for years, in banks as large as 1000 AH. As long as the bank is drawn from evenly there have not been any problems. As Maine stated it is the only affordable way to create a large bank.
 
#17 ·
I take back what I said, all I am finding is that Paralleling batt is fine. Sorry for the misinformation.

Back to the issue....I did find some thing that might help and I did not know. "If there is a .05 or more difference in the specific gravity reading
between the highest and lowest cell, you have a weak or dead cell(s). If you
are really lucky, applying an EQUALIZING charge may correct this condition."

"RECOMMENDED that you use a
temperature compensated hydrometer, which can be purchased, at an auto parts
store"

"Most of the "defective" batteries that are returned to the manufacturer during
free placement warranty periods are good. This suggests that most sellers
of new batteries do not know how or take the time to properly load test or
recharge batteries."

"Another major cause of premature battery failure is sulfation. When batteries are stored discharged or stored fully charged for over three months without being recharged"

EQUALIZING charge will fix this. This info came from this great site... DEEP CYCLE BATTERY FAQ
 
#18 ·
Series-parallel has many decades of successful performance in telephone systems and diesel-electric submarines, in electric fork trucks, and many other applications. If you follow good practice for wiring and good practice for maintenance and charging they will last a long time.
 
#20 ·
And one more for the books...
A damaged battery cable will carry less electrical energy than a battery cable in good repair. A battery cable can become damaged by mechanical stresses or corrosion. It is important, therefore, to periodically replace battery cables that are installed in an environment where there is vibration, movement, or corrosive chemicals. An ohmmeter or a digital multimeter may be used to test a suspected bad battery cable. If the ohmmeter measures a high degree of resistance in the cable, the cable should be replaced.

Sorry no scientific data to back that up.
 
#21 ·
One battery may be gassing more than the other simply because you've got something unbalanced.

That is, the cabling may not be perfectly symmetrical and same length to both batteries, so one is getting more power and boiling out faster. Or, one may be in a hotter location than the other, getting less airflow or in a position where more heat builds up.

I'd check all the gross environmental issues that can cause uneven heating before screwing around with the acid and looking for a bad battery.
 
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