In order to replace the battery in the AIO device you will need a #2 phillips screwdriver. First, loosen the screw that secures the enclosure to the wall mounted back plate (Figure A). The screw should not be removed all the way out of the enclosure, but just enough until the enclosure is free of the back plate. To remove the enclosure simply rotate away from the wall at the bottom as shown in (Figure B). Once the enclosure has been removed, turn it over to see the battery (Figure C). Next, remove the old battery and replace with a new CR123A lithium battery. Note that either of the two battery holders will work fine. The second battery holder is provided to increase the amount of time needed between battery replacements. Also take note of the (+) positive and (-) negative indicators when installing the new battery(s). once completed, simply replace the enclosure cover the same way it was removed and re-tighten the screw.