The 4000 2S Lipoly battery offers double the flight time as the stock DX8 or DX7s battery. This is a Li-Poly battery and must be charged with a Li-Poly charger. This battery will fit in your DX7s or DX8 with no modification and will enable you to fly for months without charging. No modification to your radio or the lipoly battery are required. This battery can be charged inside the DX8 with the included charger. The internal charger charges at 200 mAh so to fully charge will take about 20 hours. This battery also fits the newly released DX9!