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