Mine charges just fine from a 13.8 VDC supply. 73 Ron AC7AC -----Original Message----- Hi, I believe your PS reading is too low. The PS reading on the KX3 should be at least 13.8 volts. There is a polarity diode so your ext power supply should be 14+ volts. At least this what my KX3 needs to charge. 73 Jim H K7SSS