3* Sanyo 18650GA 3500mAH lithium ion batteries are used. The internal resistance of each cell is about 22 milliohms in good consistency. The batteries have been welded in three series, with protective plates and good insulation and plastic sealing. The foam board is attached to the transceiver circuit board to prevent collision and swing, and close the shell. Do it! Then the special 12.6V lithium battery charger is connected for pre-charging. You can always take this QRP CW amateur transceiver out to play in the future.