Looks like Nerf made a change to their rechargeable battery pack to reduce/eradicate cross compatibility with other brands. Currently doesn't fit in my Quantum, I assume I can simply cut the nub
Nerf Rival Rechargeable Battery Pack, Includes Wall Charger - Walmart.com
Nerf Rival Nemesis MXVII-10K Toy Blaster For Kids
Nerf Rival Perses Battery - Etsy
5 Reasons Why YOU Should Buy the Nerf Rival Battery Pack - YouTube