As the descriptions says: Use the charged battery on the Chron-O-John first instead of plugging it in.
Be warned this is highly missable, because once you put the battery in the plug (aka use it correctly) the game seems to autosave and you are forced to do another playthrough. I missed it by plugging in the battery immediately the first time, and realized my fault the moment after, reloaded the autosave, but it was with the battery plugged in already. And once done so, you can't pick it up again. So be warned to use it on the Chron-O-John first!