Along with cleaning the connectors, try this.
With the watch not connected, hold three buttons down (light, down and start buttons) for 15-20 seconds and try charging again.
I just finished chatting with Erica from Garmin Support Centre. The chat took less than 10 minutes and resulted in them sending me a refurbished watch, and I'll send in the defective one when I receive…
Mine wouldn't charge at ALL. I did your trick thinking it wouldn't work as there was no power left but it worked. Thank you!
Awesome thank you so much, this fix the problem. I thought I was gonna have to buy another garmin
Excellent recommendation. It worked great. Thank you
After trying everything, cleaning the contacts, pushing a combination of buttons, I used your description and voilà, it now works. Thank you for the help.
I think it depends on the aggressiveness of the sweat that corrodes the contacts. In my case, at each charge I have to rub the contacts with a cotton cloth strongly