As reyalp says you'll probably find that your batteries don't work any better without CHDK and especially it shouldn't matter much at all whether you shoot RAW or not.
But...it has been suspected and experimentally more or less verified (but not checked by firmware analysis) that on some cameras Canon requires a more from the batteries during firmware upgrade than during normal everyday shooting, making it shut down earlier if CHDK is running (remember that CHDK is started by fooling Canon's firmware upgrade mechanism). So far this has only been experienced on some dual AA cell cameras, not lithium or 4xAA cell powered cameras, though.
You can probably think of easy ways to test this. One is to charge your batteries, shoot with CHDK enabled until the camera shuts down to low battery. Then try to boot the camera to REC mode. If it fails due to low bat, then quickly disable CHDK (swap in another SD card or unlock your only card) and try to boot it without CHDK. If it boots, enable CHDK again and boot... repeat until you're confident that either it always boots without CHDK but almost always not with CHDK or that enabling CHDK makes no difference.
