Patent ID: 7911182

Claim:
An apparatus comprising a battery and a circuit powered by said battery that has a plurality of different operating, modes, wherein said circuit: operates in each of said operating modes, starting from a point in time at which said battery is substantially fully charged, said circuit operating in one of said operating modes during each of a plurality of different time intervals that are spaced from each other in time; maintains a record of how long said circuit operates in each of said operating modes, starting from said point in time; calculates for each of said operating modes as a function of said record a cumulative current drain out of said battery from said point in time to a current time; and determines as a function of said cumulative current drains whether said battery presently has a low voltage condition; wherein said apparatus includes a radio frequency identification tag, said circuit and said battery being portions of said tag; wherein said tag has an antenna; and wherein said circuit has a transmitter coupled to said antenna, said circuit transmitting through said transmitter and said antenna a radio-frequency signal that indicates whether a determination has been made that said battery has a low battery condition.