On a side note - I've just hacked power to some old ST motion sensors by using a simple switching power supply bypassing the need for batteries. Has been working really well for me.
Something like this:
And wiring that top connector to the +/- of the battery terminals on the devices. Also played around with using a usb cable + small step down transformer. Got that working as well.
I am not that savvy with things electrical but these are relatively simple low-voltage hacks. Haven't burned down the house or zapped any devices so I consider that a plus as well...
