I can't locate the receptacle for the batteries. I have had the mouse for a few years and haven't used it for about 12 months. In the meantime, can't locate the area for the batteries. The opening on the side is too small even for AAA's and as I recall it uses AA's. Even my 9 year old son, who can usually diagnose all of my tech issues, is baffled
Computers & Internet - Kensington - PocketMouse Pro 72117 Wireless 113227
Answers & Comments
PocketMouse Pro Wireless User Manual
The mouse is powered by two AA batteries found under the mouse shell, which is released by a spring-loaded, slotted latch on the underside of the mouse. A coin or thumbnail will suffice to turn the latch counter-clockwise about 45 degrees to release the back, which then pops off revealing the battery compartment.
You can see a picture here:
http://www.mymac.com/img/archives/mcpheeters/pocketmouse2.jpg
Good Luck