It can definitely handle a 3 hour run on a full charge. I used mine to send to my family on long rides (5 hours or so) and it held up well for those.

There is a 10 hr life for the battery and it connects to your phone at intervals to send out a ping to the live track, so it isn't constantly sucking energy I think.

For 3 hours it's definitely not a problem

Sweet, will give it a try. Thanks!

Do You have to run with iPhone in order to use this feature?

Yes