This attachment is part of Milwaukee's PACKOUT™ Modular Storage System, built to securely hold up to three M18™ batteries on the outside of your PACKOUT stack. It features a clip-in battery storage system and an impact-resistant body, making it ideal for fast swaps and rugged environments. The included attachment mounts lock onto metal-reinforced corners of PACKOUT tool boxes, so you can connect or swap accessories without unstacking gear.