If you don’t like to power down your Heli at every battery change, and losing your GPS fix... there is a solution.
Just install a parallel second battery connecter (can be a much smaller one), prepare an old battery with the matching connector and a Diode in the + wire as a backup battery.
(To charge the backup battery you have connect the charger behind the diode)
Before changing the main battery connect the backup to the 2.connecter, change the battery, disconnect the backup and go flying again without loss of GPS fix and so forth.
By the way I had a very successful first flight with my T-Rex450 Pro and APM2
in stabilize mode. Very stable Tail and Hover, unfortunately the weather turned bad I had to stop.
Will keep you posted.