PRCAC-HDBS275
PRCAC-HDBS350
When you absolutely, positively cannot have your battery shifting in flight, don't put your faith in the tiny little strap that came with your quad. You need confidence that no matter what moves you throw down, whether you're hitting gates or hitting loops, that your LiPo isn't going anywhere. That's why you came here.
You won't find any battery strap out there as badass as this one. It is a massive construction that will take better care of your battery than its own mother would. With this on your frame, you could smash your quad straight into a wall and your pack wouldn't even shift. (Note: You should really not do that, for other reasons.)
With a beefy metal buckle, non-slip coating, and a rubber grip, there's nothing about this strap that isn't awesome. Take your pick from 275mm or 350mm sizes.