Sorry for the late response  :-[
1) For battery on/off - you can use the standard FS command, or, set 2507004 to (L:klid). How to use klid is written in the CS737CLASSIC_MANUAL_PART6.pdf
2) APU. It's a bit more complicated. To start APU the pilot has to hold the start position for more than 2 seconds. So, set the value 2 to O17_001_SW3 and set the value 2517001 to klid variable.