Solution for batpack\jetpack armor issue

Dont wear it, make it working when placed in some predefined inventory slot, possibly first slot on quickbar.
Also you will always see how much charge it have.

ok, batpacks stay on chest slot, then to fix problem only solution without deep minecraft modificaton is proxy item...

1) Batpack proxy
2) Batpack

proxy placed on chest slot, have no durability, soo ignored in armor calculation.

actual item placed in predefined inventory slot, proxy on chest.

can be done with only few lines changed.