Do you know what? I think it's the Arduino that's the problem, not the circuit/code. Maybe the way I removed the voltage regulator or cut the LED trace. Must be some leaking current somewhere.
I have another module running off a different 3.3V step up. Not switching power off to anything. And so far the voltage is steady. I removed the LED but the reg is still there.
Not had it running long enough to work out how long it's likely to last yet.
EDITED: 27 Mar 2015 21:21 by CHRISSS