Abstract: The invention provides a method and system for managing electrical power flow among a plurality of loads or devices, which can be classified into critical loads (as to which maintaining power flow for a maximal period is a priority) and non-critical loads (as to which power flow may be cutoff when available power becomes limited). The invention is of particular use for rationing backup battery power among a plurality of data communications or telecommunications devices or services, whereby one or more less-crucial, and perhaps power-intensive, devices may be provided with a guaranteed duration of backup battery power (to perform an orderly shutdown, for instance), while a more-crucial, and perhaps less power-intensive, device is supplied with a longer duration of backup battery power, such that as the unavailability of primary power continues, crucial functions are maintained.