hey lads yet another safari radio thing

I have got my headunit hooked up with a converter all well and good but i have wacked a amp in there as well obviously i put that up to the bat and the switch off the headunit (REM) works sweet sounds are awesome but went to leave work today and it had drained my bat

didn't have anything on during the day everything was off but didn't have enuf juice to start the truck anyone else had any troubles?