7.4V 4000mAh 2S LiPo Transmitter Battery: DX8, DX9 (SPMB4000LPTX)
The 4000 2S LiPo offers not only double the flight time as the stock DX8 battery but also advanced safety and features. It also includes a built-in safety current that shuts the battery off, to avoid overcharging and damaging the battery and radio. Plus, a built-in balancing system to make sure you get the longest life and power from your pack.
Spektrum 4000mAh LiPo Transmitter Battery: DX8, DX9 SPMB4000LPTX is compatible with SPM20000EU
Built-in cell balancer
Built-in safety current prevents overcharging