Welcome to Justanswer.com, my name is Dustin.I'm sorry to hear about the issue you are having, I will do my best to help you resolve it.
If it wont retain a charge, you have one of two issues. You either need a new charger, or you need a new battery, or maybe even both.
Especially if you havent replaced the battery in 6 Years!! Its surprising it lasted this long.
You can get a charger here http://amzn.to/2d4WBv5
And you can get a new battery kit here http://www.ebay.com/itm/like/262113390399
And heres how to replace it https://www.bing.com/videos/search?q=forerunner+301+battery+replacement&view=detail&mid=0B4BC8EC226388C6116B0B4BC8EC226388C6116B&FORM=VIRE
If you have further questions, let me know
I strive to provide great service, and greatly appreciate a 5 star rating clicked and submitted when you are satisfied.. I always answer follow up questions.Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.