Nuprol Lipo battery (will fit in stock tube or in ARP-9)

Type: LiPo - Lithium Polymer
Voltage: 11.1 v
Capacity: 1100 mAh
Connector: Small Tamiya
Cell Count: 3
Continuous Rate: 20 C at 22 A
Burst Rate: 40 C at 44 A
Configuration: Stick
Dimensions: 21 x 21 x 102 mm

Capacity - LiPo Batteries have an excellent Capacity to Size ratio

JST-XH Balance Leads
1-Year Warranty
High Quality Silicone Leads
State of Charge ≥60%