Electric bikes

I don't have the equipment / knowledge unfortunately.

The battery was 3 years old when I stopped using it so would have done circa 500 charging cycles.
The battery does take the charge and shows the 5 LED out 5 on its display.
Then once placed on the bike, the battery shows one single flashing LED as if it has ran out of battery.
A jolt of e-assist comes up when you turn on/off the display.
I can reset the battery itself by continuously pressing the button on the battery (the "E" on the image above),
Then sometime it all works fine, sometimes it keeps happening.

I bought a new battery and that resolved the problem.

Now we're 3 years on and my "new" battery is doing the same thing so I want to get the first one refreshed.

I received a quote from the first Google hit but they were after £375 to re-cell it when I paid 380€ for the replacement battery in mid 2019 so it doesn't even seem worth re-celling it...