Originally I just used velcro strapping through some of the slots in the back plate. It was a bit of a PITA to strap up individual batteries every flight and I wanted to go to eight. I went with a shelf system.
There’s no provision for jettisoning the packs. If they got that hot they might burn the strapping and tape then fall away. Or not. 
I also have no additional impact protection for the batteries but anything that might hit them would literally have to come through me first 
so…?
The system is light, safe, simple, and easy. What else does an aviator need?