Not totally true… Wet type emergency lighting batteries always consume some of the electrolyte (sulfuric acid for lead and potassium hydroxide for nickel cadmium) when they are being charged. The need to refill is based on age, ambient temperature, charge rate, etc. and the established monitoring of properly maintained levels of liquid. The charging process normally produces a flammable gas mixture of hydrogen and oxygen. A short circuit, open flame or smoking during must be avoided when adding water to keep the fluid above the plates or the battery manufacturer’s indicated max fill level. Some maintenance free batteries that use calcium instead of lead require less maintenance because of the greater reservoir capacity. Adding distilled water where and when possible will greatly increase the life of these “so called” maintenance free batteries.