I weigh my UPS battery every year and compare it to the original weight that I had printed with a label maker. Over the battery lifetime (2-3 years), there had

I weigh my UPS battery every year and compare it to the original weight that I had printed with a label maker. Over the battery lifetime (2-3 years), there had been around a dozen switchovers, and the only reason of failure I could think of is the electrolyte evaporating because of a warm interior of the UPS. This gives me an idea, of how much water is lost, and at a certain cutoff, I just replace the battery.