Uninterrupted power supply for DC-distributors, which must continue to work in case of a power failure, such as for alarm units, telephone systems, automatic door openers, production & process control systems the DC-UPS units are indispensable. Alternatively, an external lead-acid battery or one or more EA-BU units (maintenance-free, gas-tight lead-gel batteries) can be connected. Power failure & low voltage of the battery are reported via LEDs & potential-free contacts. In case the emergency operation goes on for so long that there is a risk of deep-discharge, the device is switched off. Through pluggable connection terminals the wiring is pre-fabricated or the maintenance & exchange can be done very quickly. The changing & maintenance of the accumulator batteries can be done during the mains operation (trickle charging).