Sadly but I think it has to do with airline safety.
Removable batteries can cause problems when damaged due to it being 'a moving part' and recently lithium batteries had been limited and inspected for safety (you can't carry non-OEM battery or too many powerbanks in flight, even extra laptop battery) that is due to it being so volatile that a puncture when full charged can cause it to blow and fire up.
This is why you need to use shim to have access because pooniggers gonna nig. Also the part where Reyat would use such device as a detonator is a possibility
en.wikipedia.org
either way it's pretty easy to source lithium from chinas as they are so into this scene right now. your only problem is safety/temperature sensors if you 'diy' your own battery.
F(x)tec Pro1
Ethan Moore
Brandon Gonzalez
gpd pocket 2.