Most DC-UPS systems use two 12V batteries in series to backup 24V applications. However, this method does not allow the two batteries to be individually charged or monitored. Instead, only the sum of the battery voltages is measured which leads to one battery being overcharged and the other battery being undercharged. The voltage difference between the two batteries will increase over time, significantly reducing service lifetime and can cause damage to the batteries that could shorten the backup time during a power loss.