I charge my Forerunner 405 to a 100% before a run, but within 20 minutes of starting the screen goes blank (less for the Garmin software info) and it beeps until the battery dies completely. I've had it 5 years. Can it be fixed or do I need to replace it?
That is probably a good question for Garmin Support. Contact information is available on the support page. Also, this post really belongs in the Garmin 405 forum.
I believe that garmin will replace the battery for a fee - (assuming the watch is not still in warranty) - if you email support as per the comment above they should give you a price
