Hm, usually on the underside of the head is a round "plug" with a slot in it. Put a quarter in the slot and use use like a screwdriver; turn the plug 1/4 turn. The battery sits inside, or behind, that plug. Usually.
THANKS, MADPOGUE! I finally figured out how to detach the computer portion from the base that attaches to the bike . . .
Does anyone know where I can get a replacement manual/instructions? I lost all of the data and I'm sure the settings when my battery went dead! I think I need to reset the config. for the wheels. I also was always off previously. I see one guy who was off my 12%. How close do ya' all have your sensors . . . close to the rim or center of the spoke? I'm sure that placement would affect the degree or error ratio.