I'm using this battery pack on a 29'er MT bike with SP Dyno hub, Garmin 810 and iPhone 5c. I can have the Garmin charging while the dyno hub is plugged into the battery and the Garmin doesn't try to turn off when I slow below charging speed. So, I'm charging the Garmin and adding power to the battery at the same time. Perfect! I've only done a couple hour test ride and don't know how all this is going to work 'for real.' I'll be riding the GDMBR next week. That should give it a good test. If I can do it I will report back. Great customer service too when I was asking questions.