If the checker works on your charger but not on your battery pack I would suggest that your battery pack is not putting out enough voltage to read. I checked the part number and the checker is rated for the 5 cell packs. I am also not sure wheather you should have modified the wiring as the Red wire is supposed to be on the inside connection and the Black is upposed to be in the outside connection. The unit comes like this when you buy it. If you wish to stick with the Cirrus brand the unit you need is part # 444762. If you look at the pics you will see that it says for 4 cells. The unit you have says for 5 cells. You hobby shop guy should have picked up on that! [8D]