Once the LiPo was installed into the stock compartment, we found it difficult to fit the MOSFET, fuse and cables back inside without the risk of overbending (which weakens the circuit over time). Likewise, we wanted to minimize the prospect of denting the battery's surface from the cramped spacing. By offering additional spacing inside the compartment, the Battery Extension Unit (BEU) is designed specifically to relieve all stresses on the ARP9's components, while protecting it throughout to extend its durability. There are crevice's on each side of the BEU to maintain a constant flow of ventilation to the battery and components to prevent a buildup of heat. The BEU is designed to fit beautifully with the ARP9's original design by sitting seamlessly inside the stock compartment with no modification needed to install. Made of strong, flexible nylon that is resistant to BB impact and rough handling.