[TheReferee]

extract from the rules

25.6 LiPo/LiFe drive batteries must be charged in a ‘Lipo sack’ at all times.
LiPo sack is defined as a receptacle designed for the purpose of charging LiPo/LiFe batteries and of a suitable construction as to contain a LiPo/LiFe fire.

an "ammo box" is a receptacle which is capable of containing a lipo fire, therefore its allowed, you could argue that it wasn't designed for the purpose in the strictest definition of the rule. however it is assumed a certain degree of common sense is out there. clearly a tesco bag would struggle to comply with both the design and containment parts of the rule.