I only use it when I travel on holiday, so really

I only use it when I travel on holiday, so really havent used it that much...but I found in the last year, the thing would switch off, as the battery had run down, even though it was still connected to the mains charger. When I wiggled the connecter in the top of the player, the green light would come back on after a minute or so, and then give the indication of charging, with the flashing light. BUT, the battery doesnt seem to take any charge ...it doesnt charge up. and if i just keep the mains cable connected, the green charging light will suddenly and randomly, stop. By the time I spot it, the battery is 100% flat, and I am back to square one. So thinking it was a new battery needed, I just purchased one on line from battery mill, in london. It arrived three days ago, and nothing has changed. So, by deduction, its not the battery that is at fault, and I have sent the new battery back today for refund.
Therefore I am back to square one, with the problem and no idea what to do next.
any ideas/suggestions?thanks