Flooded Batteries (batteries with liquid in them) require the addition of water periodically to take the place of the water lost to evaporation. Both lead acid and Ni-cad batteries require periodic additions of water to keep them hydrated and healthy. But what kind of water and when do we add it?
The ONLY type of water you should ever add to your batteries is water that is free of minerals and chemicals. This type of water is achievable at your location by the use of a battery water filter/deionizer that can be purchased and installed in your battery room or by the use of distilled water. Only these two types of water should ever be introduced into a battery. NEVER use tap-water under any circumstance.
Tap water is treated with chlorine and fluoride and has various amounts of minerals dissolved in it. The amounts depend on where you live. You’ve heard of “hard” water? That’s a term that refers to the amount of dissolved solids like limestone, calcium, etc. that’s in your tap water. For instance, in West Texas, the water contains petroleum products, in addition to minerals and chemicals. You definitely do not want this in your batteries.
Chemicals and minerals can “poison” your batteries and cause them to degrade over short periods of time. We’ve used the term “short-life” in previous entries and this is just another item over which you have control to insure the maximum life from your batteries.
So ONLY use deionized and filtered water or purchase distilled water to use in your batteries. As far as filling your batteries, only fill your batteries to ½ way between the high and low level marks. This allows for batteries to expand and contract and charge and discharge without “pumping” or spilling of the electrolyte (water+acid). You should only have to add water to your batteries every 30 to 45 days (for backup power batteries). If you’re adding water more often than that, you might want to have a battery specialist come take a look at your system to determine the cause of high water usage by your batteries.