Forum Discussion

profdant139's avatar
profdant139
Explorer II
Nov 02, 2020

Battery water falls very slightly in Cell Six?

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 Plu...
Gdetrailer's avatar
Gdetrailer
Explorer III
Nov 06, 2020
profdant139 wrote:
These are five year old marine batteries -- they have never dropped under 12.1 volts, measured while resting. Always topped up. Not a hint of trouble so far.


5yrs? They are in the "prime of their lives", no reason to worry at this time, should be able to get another 5 yrs as long as you promptly recharge after being discharged and don't mind a slight lower capacity towards the 10 yr mark.

profdant139 wrote:
Based on the consensus of the posts above, it looks like I should not worry about a tiny drop in the water level of one cell over a period of several months.


CORRECT!

The cells are not 100% perfect, each cell will use slight different amounts of water which is normal and to be expected.

Think of it in a different way, in everything we humans make, there is a "tolerance", that tolerance can be graphed and you will sell a "bell shaped curve". As long as everything stays within the bell shaped curve tolerance all is well. I suspect you find it to be very rare that everything made will hit the center of the bell curved 100% of the time.

For more information on bell curves you can look and read up on mathematical statistics.

profdant139 wrote:
And someone wondered whether I really meant that it was down by a half ounce. That's really true. I measured how much I had to add to the cell to get it up to where there is a "meniscus" at the bottom of the fill tube. That's the curved lens shape on the top of the water.

I have been told that you add water just until that meniscus appears. If that's wrong, I am sure someone will let me know!!


The closer fill to the top actually can cause excessive water use/loss, my Dad taught me to fill to JUST BELOW the fill ring (not touching or not up in the fill ring). This gives the water bubbling up some breathing room when the bubbles break. Keeps the splashes lower and less chance the caps will get a lot of liquid on them which results in liquid being forced out the vents..

Overfilling is most likely a big culprit for terminal corrosion that some folks complain about.. I don't have that problem as you can see by the pix I posted.

In a nutshell, as long as the water is above the plates and just below the fill rings you are good to go.

Never want the water to get below the tops of the plates, that exposes the plates to the oxygen in the air and will degrade the plates fast.

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