i.e. removing the power-hungry components.
What components are these?
to quote from Nick Gammon's article....
huge overhead of the voltage regulator and USB interface chip.
Basically, Nick suggests building up a bare-bones board from scratch, I was wondering if it would be easier to start with a off-the-shelf development board and strip it down.
Why don't you use some solar cells to top up the batteries?
The environment I'm monitoring is inside a vehicle parked inside a barn. - it doesn't get much sunlight.
To be honest, the easiest solution is probably to use a bigger battery and visit it more often to check it's charged ok, but I'd prefer a more elegant solution if possible