charging and battery draining on iwatch series 3

I have over last day or so found that my watch is suddenly only charging to a maximum of 39% and no more....then I can literally watch the percentage drop as if it were a countdown timer!! I have tried hard restart, turning off and on again, unpairing and then pairing again. I am up to date in terms of updates.

The green charge symbol is showing??? I'm at a bit of a loss any ideas gratefully received.