disclaimer this worked on my op-z, it may not work on yours. i hope it fixes yours, but if things go further south, i am not responsible. research and make an informed decision.
hi! i tried to use my op-z after putting baby in a corner for 6-8 months. when connected to usb power it worked great, showed 100% battery in the app, and had a solid led indicating it was fully charged. this, however, was not the case. upon disconnect baby no bleep. multimeter confirmed death… or was it just a coma!
after digging a bit, i came to the conclusion that the protection circuit got tripped. bereft of a specialized charger, i decided to try parallel charging from another 3.7v LiON battery (this was a cell out of my blindy-tron 900 flashlight) to bump just enough pixies across to unlock. i stripped two short lengths of solid core hookup wire and used a rubber band to connect a wire each to the + and - (did not want to solder/did not have magnets). i then touched the wires to the + and - contacts on the op-z battery for approx 15 seconds. slapped the batt back in and put her on the mains. charging led went blinky blink (and i got a full charge)!