I've been using my S60 for over a year with no issues, however came to put it on to play yesterday and battery was at critical level which was very unusual because i charged it in the week. So i charged it fully during yesterday afternoon and then unplugged it. Went to put the watch on today and again the battery was at critical level...
I haven't - as far as I'm aware - downloaded anything or in fact even touched it between it working fine and then the battery having issues.
Im currently using v6.10, and apparently it is up to date.
Any one have any thoughts on what might be the issue?
Have you tried contacting Garmin support? Batteries can go bad in any device. Not sure with the S60 but with most devices Garmin offers out of warranty replacements for pretty low price. They may even be willing to still cover it under warranty.
With your S60 unplugged, hold down your middle right power button for 1 minute. If no response, try charging it again to see if it will charge. If still not charging, while plugged into charge, hold down your power button for 1 minute again. If after these steps you need further assistance, please contact your local regional support by going to our Garmin International webpage and selecting your country on the bottom left corner. Once there, go to the Support Center to contact Product Support.