I had customer with an Acer Spin 5 (SP513-51) that would charge the battery and show it as 100% charged but as soon as you unplugged the AC power the laptop would turn off.
Turns out that there were a few screws missing on the back of the laptop and on this particular laptop one screw is critical to to keep a tiny microswitch pressed in, via the back cover, to keep the laptop on when using battery power.
See the picture below:
- The orange circle shows the microswitch. If this switch is not pressed in the laptop will not operate on battery power.
- The green circle shows the critical screw that needs to be there (through the back cover) and tightened.
- The blue circle shows another screw hole that should be clear of the black power cable.