Focus Jam2, 6.8, 2019 Battery or Charger problem ?

[Prostu2]

I just bought a used Jam2, 6.8, 2019 bike. It has 1520 miles on it.
The range was saying it had 37 miles left. I put the charger on and left it run overnight. This morning the charger was still flashing green colour, when I think it is supposed to be the fully charged bar below the flashing light that is lit when fully charged.
I then went out for only about 1/2 mile, put the charger back on, after maybe an hour the green flashing light suddenly went red, this is the hazard warning lit up.
I do not have the manual for this bike.
Does anyone know why the charger is not displaying fully charged ?
It has me thinking the battery might be faulty, or the seller suggests the charger might be faulty ?
Any ideas or knowledge would be appreciated. I only bought the bike yesterday

 

[Peaky Rider]

Your first step is to try a reset which is a bit of a pain as you have to open the battery up.
Several threads on this problem. If you scroll to the very bottom of this page you should find them.