You're not the first person that's asked for this, so definitely I think it will need to be included at some stage. At the moment, you could set the system to run tests manually, though it will still run background builds (thus churning up your battery).
Although I've never really tested NCrunch much on batteries, I'd expect that much of the power drain is probably because of the hard disk activity. The constant background builds will spin the HDD up constantly. A way you can reduce this (if your solution is small enough) would be to try configuring NCrunch to deposit its workspaces onto some kind of virtual RAM drive. You'd need to get hold of another piece of software that can create the virtual disk for you, but I have seen this work very well before.
