Not all battery cells needed water, unusual?

[Silver_Is_Money]

When I added water to the cells of my batteries today (4 x 6 volt, 24 volt system) I noticed that some cells needed water, and some didn't. Is this to be expected, or is it a potential sign of concern?

[organic farmer]

It would be a good idea to log this. Basically just a sheet of paper to write down which batteries did not and which ones did. Do this every time you check the batteries. If any battery needs water all the time, that may indicate the battery is getting ready to die.

Unfortunately when you end up replacing any battery, you are pretty much obligated to replace all batteries at the same time.

[Silver_Is_Money]

For each battery there was at least one cell that did not require adding any water.

[paulcheung]

If all the cell has the same amount of the water at the beginning. it is a bad sign. mean they are not been charge the same. those whose don't need water are dying. that is my experience.

[Silver_Is_Money]

Thank you paulcheung!

[Wy_White_Wolf]

Cells toward the outside of my bank usually take less water then internal cells. I attribute this due to them being able to dissipate heat faster and easier than the internal cells. Not anything I can change or do much about.

WWW

[inetdog]

One can speculate that the cells that have not needed water have a higher self discharge or a lower charging efficiency. They may be getting just as much of a charge, but if they started low for some reason and were never equalized they will not reach the gassing voltage threshold as quickly as the others and so lose less water.

Two contradictory explanations:

1. The high water cell is failing (high self discharge, lower effective charge rate).
2. All the rest of the cells are failing (low capacity because of sulfation) and the high water cell is the only good one. It will eventually lose capacity until it matches the rest.

Which happens most often is a question of practical experience, and the first step to see what is really going on is to apply a equalizing charge, not just an extended absorb.

[Sunking]

Not unusual, it is normal and part of the charging process. It is a necessary evil. Many factors contribute to water loss, but it all boils down to the charging process. In order to fully charge a daily cycle battery, you have to reach Gassing Voltage. Excessive water use most common cause is operator error by over charging.Another common cause is 1 or more cells is weak or defective. The weaker cells reach gassing voltage before the healthy cells. Thus will use a lot more water than the others. A battery hydrometer will spot the problem cells and tell you what to do.

Good luck