Battery power system

The present invention relates to battery power system configurations, particularly systems using VRLA batteries in uncontrolled environments wherein the batteries are isolated from the rectifier when the batteries are in the float mode but on line during charge and discharge. The battery power system configuration of the present invention eliminates thermal runaway because the current drawn by each battery is limited to the value determined by a constant current source. A shorted battery cell may be easily detected by observing if the voltage of the battery is lower than a specified and expected value. In addition, battery capacity is maintained by the boost provided periodically from the current source. Finally, batteries are protected against receiving excessive current and since the currents sent through the batteries match the needs of these particular batteries, the life of the batteries is increased. Moreover, in the event of AC power failure, transfer to the battery power system is immediate, in other words, the transfer time is zero.