Connected to my 12V AGM battery. Measured with a good ammeter, it charges at 8.7 A and the display shows 9.2 A. I was expecting 20 A. The display shows a voltage that is 1 V higher than the actual battery voltage. The % charge display jumps between 7% and 12%. The thin DC cable becomes hot. I'm re-voting this because it's not working as advertised and I wanted more relevance.