Why does my MacBook require battery removal to restart?

I have a MacBook which shuts down and then requires the battery to be removed and replaced before it will restart.

When it is in the locked state, the charger indicator light does not illuminate. The battery level indicator also does not illuminate.

Once the battery has been reconnected, it works as normal for a few weeks.

The last time it locked up, it was connected to the charger and was charging overnight.

Coconut battery shows that the battery is at 80% of design capacity.

The OS indicates that the battery condition is 'Normal'

It has a cycle count of 643

Since the last 'lock-up' I have reset the SMC and PRAM, also repaired disk permissions.

The OS is 10.10.5

Is there anything else that I can check/do to resolve the problem?