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Battery water falls very slightly in Cell Six?

profdant139
Explorer II
Explorer II
I usually check my battery water every month. (These are group 31 flooded marine batteries from NAPA.). I almost never have to add any water.

I keep the batteries hooked up to a Battery Minder Plus, one of those pulsating things.

This summer and fall, due to some fairly serious medical issues in the family (but not my immediate family), I skipped my usual battery water ritual for about four months in a row.

When I checked them the other day, five of the cells on each battery were fine. On both batteries, the sixth cell (the one nearest the positive terminal) was down about a half an ounce -- almost not down at all, but still different from the other cells.

The specific gravities of the cells were uniformly good, according to my tester.

I'm not worried about this phenomenon, but it is puzzling. Why would one particular cell lose a tiny amount of water?
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24 REPLIES 24

Gdetrailer
Explorer III
Explorer III
BFL13 wrote:
My battery book says charging is also an oxidation process that corrodes the positive plates with prolonged overcharging (as when the float voltage is a bit too high I guess).

The positive post is to the first positive plate in series in the battery, so would it get corroded more than the others and would that make for more gassing from its cell than from the others?


Doubt it, otherwise every single DC connection would have the very same issue.

Terminal corrosion typically comes from battery acid, this can come from excessive over charging resulting in excessive gassing and the battery must vent that. The venting vapor will have residual acid in the water droplets that are vented (the reason the Gel or AGM batteries do not have this issue, when those batteries have to outgas you have done something badly wrong).

Poor or bad seal on the terminal to battery case can also cause corrosion, typically the POSITIVE terminal in most automotive applications. On older vehicles the positive wire was extremely short since it went to the solenoid mounted beside the battery. This didn't give enough slack for movement and vibration.. Eventually over time the terminal to battery seal would fail and acid would creep up the terminal (wick). The negative terminal seal typically did not fail because that wire ran to engine and frame and had lots of slack.

I have experience this issue with older vehicles and even a tractor, new vehicles since the 1990's I have never had a terminal corrosion issue.. Coincidence? I don't think so, more modern vehicles MOVED the starting solenoid to on top of the starter.

Since terminal corrosion and all that hard work it is to take care of FLA batteries subject comes up often I decided to take a few photos of my GC2 batteries while I was checking the water this fall..

Ignore the water on the top, pix were taken AFTER I added the water.











For the record, those are Extra flex 1/0 cables so they are far less stiff (1000+ little tiny strands of fine wire)than what is in a automobile or even on your RV connections.

Those batteries were installed in 2017 and the terminals are so clean you could eat off them.

I did use a small dab of "OxGuard" per connection which is same as "No-Alox" which is used for electrical terminations with aluminum wire to electrical panel terminations. I have also found OxGuard works great for any electrical termination that may be exposed to high humidity or outdoors..

On edit, I should also note that this trailer sits only 10ft off a busy road, it is below the road level and road is heavily salted in the winter (salt spray is so bad that I have to take anything made of steel on my home front porch in for the winter) so some of the steel bolts have some rust and the homemade terminals I used are soft copper pipe with two layers soldered together for good measure.. The solder is showing some weathering and copper is not as shiny, but hey, it has been 12+ yrs with that setup..

BFL13
Explorer II
Explorer II
My battery book says charging is also an oxidation process that corrodes the positive plates with prolonged overcharging (as when the float voltage is a bit too high I guess).

The positive post is to the first positive plate in series in the battery, so would it get corroded more than the others and would that make for more gassing from its cell than from the others?
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MEXICOWANDERER
Explorer
Explorer
Ponder This Dept...

Ford motorcars as far back as 3 cell batteries almost always corroded the positive terminal on the positive grounded battery. I thought this may disappear when Ford electrical systems changed polarity and voltage in 1956, but it didn't. Tar top batteries did not change things. Remember pennies stuck in the tar? The days of baking soda followed by a glob of grease. And all batteries were deep cycle. Kids. Park on a grade with a young lady turn on the radio listen to the vibrator when the tubes were warming up and silently curse as crashes of lighting static screwed up Fats Domino or Chuck Berry. While the positive cable slowly corroded.

Gdetrailer
Explorer III
Explorer III
Such obsession..

There is no "perfect" battery, every one will have cells which will vary how much water is used slightly, at the end of the day, 1/2 ounce is peanuts.

I don't dote or obsess over my batteries, I only check them ONCE A YR, typically in the spring before we start camping. This yr due to the virus, we didn't camp.. So, I didn't bother checking the water..

Recently decided to check to make sure TT is ready for winter I checked the water..

Took about 2 ounces per cell for a yr and half sitting on charge with my PD9160 with Charge Wizard.. I do not directly measure exactly how much water I added to each cell, I use store bought 16 oz bottles of water.. This yr only used ONE 16oz bottle over all six cells.. I add only enough to get close to the fill ring.

In my case, top of the plates were not exposed and that SHOULD be what you are concerned about.

Replaced my last set of GC2s at the 9 yr mark and they were using average of 4 ounces per cell (TWO 16 oz water bottles)and not holding as good of a charge as I wanted.

As long as you have a decent charging setup which drops to 13.2V your batteries will not use much water.

Your batteries are fine, don't sweat slight differences in water consumption, just don't allow the water to drop below the top of the plates and you are good to go for a long time.

time2roll
Nomad
Nomad
I agree it is a sign of the cells getting out of balance. How old is the battery? Could yet have a long life ahead. Half ounce is hardly enough to lose sleep over. Probably get worse over the next six years.

Ed_Gee
Explorer II
Explorer II
Let me rephrase - one cell starting to use more water than others was a very early symptom of battery starting to think about going bad...... not to say you don't have another year or so of good life. The fact that the SP of all cells was good and equal indicates nothing to be immediately concerned with.
Ed - on the Central Oregon coast
2018 Winnebago Fuse 23A
Scion xA toad

MEXICOWANDERER
Explorer
Explorer
Like using a thermometer and finding temp at 98.7 F

Lwiddis
Explorer II
Explorer II
Half an ounce?
Winnebago 2101DS TT & 2022 Chevy Silverado 1500 LTZ Z71, WindyNation 300 watt solar-Lossigy 200 AH Lithium battery. Prefer boondocking, USFS, COE, BLM, NPS, TVA, state camps. Bicyclist. 14 yr. Army -11B40 then 11A - (MOS 1542 & 1560) IOBC & IOAC grad

Ed_Gee
Explorer II
Explorer II
One cell using more water was the first sign I had of my wet cells going bad.....
Ed - on the Central Oregon coast
2018 Winnebago Fuse 23A
Scion xA toad

Lwiddis
Explorer II
Explorer II
Half an ounce wouldnโ€™t, doesnโ€™t, concern me. Iโ€™m a Trojan guy...batteries and university. lol
Winnebago 2101DS TT & 2022 Chevy Silverado 1500 LTZ Z71, WindyNation 300 watt solar-Lossigy 200 AH Lithium battery. Prefer boondocking, USFS, COE, BLM, NPS, TVA, state camps. Bicyclist. 14 yr. Army -11B40 then 11A - (MOS 1542 & 1560) IOBC & IOAC grad