Bulk export

have a look at
https://tapiriik.com/

"tapiriik synchronizes your fitness activities between Garmin Connect, Runkeeper, Strava, TrainingPeaks, SportTracks.mobi, Endomondo, RideWithGPS, TrainerRoad, Motivato, Velo Hero, Epson RUNSENSE, Dropbox, and Smashrun
(your heart rate, cadence, power, and temperature data syncs too)"

If not comfortable with giving away passwords to 3rd party sites like that, this javascript can be run on your browser locally and is simple enough to see that it's not doing anything nefarious with your data or try to steal your cookies or anything. All url calls are to Garmin Connect and nowhere else.

Code linked below:

http://pastebin.com/YN6Gex5R

bulk export

Thanks lightmatter, I gave this a shot and after a couple of stumbles I successfully got 30+ kml files from my activities on GarminConnect. Thanks for sharing.