The most common reason for exit sign or emergency light failure is an exhausted battery. Unfortunately, backup batteries do not work forever. Rechargeable batteries, after a while, lose their abilities to fully charge. To keep your signs and lights in compliance with the 90 minute backup required, a replacement battery is necessary. The Exit Light Company carries a wide variety of replacement NiCad batteries, 12 volt sealed lead acid batteries, 4 volt sealed lead acid batteries, 6 volt sealed lead acid batteries and UPS batteries.