Methods and apparatus for conserving battery energy used in transmitting signals carrying data from a downhole location, using a transmission system where a predetermined set of data is to be transmitted once during a predetermined period. The method can comprise the steps of: transmitting at least one signal during said period to transmit the set of data; selecting the time of transmission of said at least one signal; and representing at least some of the data to be transmitted in terms of the time of transmission of said at least one signal.