here is the point for hard case..

if you use a box.. it must be same sizes as soft pack.. so Zero movement inside box..

if it can move.. it will scuff the soft case till it leaks... and a sudden fire will happen.
reason all pre lipo rechargeable batteries were hard cased, aka sub-c and all others..

rechargeable batteries are made with powerful chemicals and most HATE Air... and react badly with it.

my opinion.