It looks like they are going to speed it back up after we complained about it a bit:
It is weird that you are seeing background operation issues. I actually did an entire mapping run the other day while I was on the phone and was surprised how well it did... Please verify your build number and send us your phone specs offline. We thought we had that pretty nailed.
The time limits we have added in the settings are for planning estimates only. Our next release (after 150825) will have it trigger coming home after the specified time was up. If you would have let it go it would have come back at 18% or earlier if it needed the juice to return. That is the default DJI setting for it coming home. The warning is just the beep on the remote and we don't touch that setting since people like to set that all over the place. There is a second, more serious warning at 20% and then it will generally head home no matter what at 18%.
We have let it run down A LOT of times on the same set of batteries with no issues. Yet...
At any time, you can hit the Go Home button and the next battery will pick up where you leave off.