For VRLA batteries, annual discharge test initially became the preferred method for measuring battery capacity and for assessing its condition. This remains the most accurate, but also the most expensive, way to check battery condition - and is valid only at the time of testing.
The remaining battery life cannot be predicted. In recent years, improvements in the design of the VRLA battery and the high cost of discharge tests have led many users to look for ways to reduce their maintenance regime and costs. One of the old techniques, used in place of full discharge, was a partial discharge using site load. This method has a major weakness in the fact that many faults may still not be detected until the accepted battery life limits are exceeded. One needs also a special local test system.
Thanks to today's technologies, there is availability of better options for current practice for same battery test year after year to check the condition of the batteries in real time (i.e. Adelsystem has a specifically internal system, which does not require external systems). A condition-based maintenance program uses tests that are best suited to the age and the current condition of the battery. This would typically involve regular low-cost techniques that provide an acceptable indication of the health of the battery at the beginning of its life cycle.