Momentary to Latching Circuit with Zero Off Current
Depending on the requirements you could use a latching mosfet circuit as shown below. The first time you push the button M1 is turned on, the second time you push the button it is turned off. 

When the circuit is off it does not consume power (other than leakage of the mosfet). 







simulate this circuit &ndash; Schematic created using CircuitLab