Battery Acid Build Up

Copied from Battery Boys website (US) .........

Corrosion and its affects on battery performance

The recharging process of batteries produces gassing as a result of the breakdown of oxygen and hydrogen gas. This is the primary factor that causes corrosion on your battery cables, terminals, and other battery related metal parts. During charging, the gas that escapes through the vent caps, bringing with it small particles of sulfuric acid which are heavier than air, drop and form corrosion on your battery cables, terminals, battery hold down rods, nuts and bolts. This acid settles on the top of your batteries and eventually makes its way down the sides of the batteries to your golf cart’s aluminum or steel battery tray.
You will see a very corrosive white powdery substance on your battery terminals, cables and other metal parts in areas near your batteries. Corrosion probably will also be on your battery tray and on the garage floor. This corrosion can even travel inside your battery cables causing high resistance and improper charging. The corrosion that forms on your battery tray will eventually deteriorate the aluminum or steel battery supports and could cause your batteries to drop through the bottom of your cart. It is common to see the battery hold down rods, nuts and washers completely eaten away if corrosion is not managed properly and in a timely fashion.
How does this happen? There are several reasons. If the batteries are over filled or filled before they are charged, the electrolyte expansion forces some of the liquid out of the vent caps or past the vent cap gaskets on to the top of the batteries. Some batteries have vent caps that leak due to poor design. Trojan Battery Company has a proven and patented vent cap designed with a manifold that captures the condensation of the gas and then drains the liquid down the center of the cap back into the battery cells which practically eliminates all leakage and helps reduce water loss.
As batteries age their voltage drops and require longer charging. During charging, these batteries get warmer and gas more, forcing the gas out of the cell vents or past the vent gaskets. In some cases where certain poorly designed single point battery fill systems have been installed, the fill system’s gaskets become distorted causing leakage or the watering system’s valves have failed to work properly causing leakage, under filling or over filling.

It would seem your issue is caused by venting of the battery as the battery terminals are not affected. This could result as posted above by overfilling or overcharging of a cell/cells.

If both batteries are similar then it would tend to indicate one battery has a faulty cell/cells. Try measuring the battery voltage during charge and after the batteries have been standing for 24 hours and see if there is a marked difference between the battery with the corrosion issue and the other. If the battery with the corrosion is lower than the other it would tend to indicate the battery is faulty.

Thanks HBK I'll do those checks over the next week or so.

Shaker, Thanks for the effort to write up that informative article.
Could well be the gassing no other explanation really.

some thaughts
A/ are both batteries identical and the same age?

B/ are the batteries in paralell, series or are they seperated by some sort of charge controller?

C/ are the batteries unsealed wet cell or some form of sealed battery.

D/what is the charging voltage of each battery

All unsealed wet cell batteries vent, explosive gasses and acid vapor every time they are charged ... in a vehicle that means every day they are driven ... ... All so called, sealed batteries including ALL AGM will vent explosive gasses and acid vapour when over charged, or operated above design temperature.

Batteries may also tend to vent more gasses and acid vapour than normal in the later part of the life.

These days I will not buy an unsealed screw top battery for use in a vehicle ... they are mostly just bad value ...... the sealed maintenance free batteries have a number of advantages over the cheaper screw top batteries. ... then there are other types of sealed batteries .... the issues remain to a greater or lesser degree

One of the biggest advantages of sealed batteries is they do not vent acid every single day they are used like screw top batteries do ....... this results in a far cleaner battery installation and near enough to no corrosion problems.

It is also far from uncommon for the seals in batteries around the vent, vent valves and terminal posts to deteriorate with age.

One thing to consider is, that it is common to bump the charging voltage up to get the best out of sealed batteries ..... the problem is that if running over 13.8 Volts, screw top batteries WILL vent excessively.

Older vehicles mostly had their charging systems set at 13.8 volts ... this was the best compromise for screw top batteries ....... later model vehiclesand most replacement alternators run higher charging voltages typically 14.2 Volts ..... people also sometimes fit booster diodes to raise the charging voltages of older alternators.

just some thaughts

Cheers