The most important characteristic to consider when purchasing a deep-cycle battery for a renewable energy application is cycle life. This is usually measured as the number of discharge/charge cycles the battery can provide before its capacity drops to a specified percentage of its rated capacity (i.e. 50%). Batteries from different manufacturers may have the same capacity and energy content and be similar in weight, but design, materials, process, experience and quality control have a big influence on how long the battery will cycle. When comparing two batteries of equal Ah capacity and cost, a battery capable of 1,000 cycles is effectively half the total life cost of one that is only capable of 500 cycles.