The first Android devices, Lenovo A1 tablet was left aside for a few weeks . Recently I tried charging the device , after a few minutes, the screen will light up saying “Battery is illegal” in English and Chinese. Then the device shuts down.
A quick noodling around, reveals that this is illegal battery problem is quite common, except the repair method is uncommon. The Lenovo A1 does not have a removable back. The repair method is to unplug the battery, wait for a while and plug back. The various U Tube videos showed a guy opening the back with his fingers, and another using a guitar pick. I tried using a normal credit card but it was too thick, so I put my expired IEEE membership card to good use. It is a plastic covered cardboard and about half the thickness.
I ran the card round and round the table to free up in the internal plastic catches. Took some time as I did not want the back to break. After a few tries, I managed to take the back off. The battery is connected via short cable. Unplug it and wait for a few minutes. Plug it back and charge. After a few seconds the charging light started blinking. Several minutes later the green battery bar showed up on the screen showing 1%. Do not install back the cover yet.
After overnight charging, the device can be turned on. Did a quick check through, looks like it is back. Popped the back cover on.
Lenovo maintenance manual link