Forerunner 910 not charging but watch says charge 100% complete

Hi, my Forerunner910 is not charging but when connected to the charger says it's 100% complete. If the watch is connected to the charger I can view activities and history but as soon as I disconnect it turns off and shows an empty battery symbol. 

When charging it also shows the plug in sign rather than the battery charging symbol. 

I've tried hard reset and it makes no difference. Have any of you had similar problems and been able to resolve them? 

Thanks  

Jake