This extension can download multiple activities from Garmin Connect
Image from store
(2020-07-29) Lukasz Slowinski: Great tool. Helped backing up all my Garmin Connect activities after the Garmin crash. It is not faultless. I noticed that if you have a manually entered activity or if you added your weight to your runs, it will stop importing. You will need to start again from the run after the activity. Having said that it is still very useful.
(2018-02-18) Dipankar Paul: Wonderful tool!! Thx. Helped me save a lot of time and learnt a bit of JQuery tricks as well..
(2017-11-13, v:1.5) Eddie Dean: update garmin.com/express