discharged ones are red in the lower row

The far left pin is negative so plug it in so the black wire goes to this left negative pin. On the left side it has the negative – symbol so you can tell its plugged in correctly. It will make a lot of noise while it determines the cell states. Charged cells are green at the top and discharged ones are red in the lower row. When we plug in the alarm there is a spare pin on the far right because we are using a 3s(3 cell) battery and the alarm supports up to 4s (4 cell). So connect from the left – negative to the right positive and next to that will be our spare.