If you ask me a lipo sack is a complete waste of time and money, purely because the Velcro "seal" cannot close properly when your charging wires are going through it! All you would get if the lipo went up is a space shuttle sized flame shooting out the side of the bag, probably straight into your crotch
I would rather be able to see the battery charging and give it a quick feel every now and again to make sure it's not getting warm