When one dead battery is in the first bay #1, then the green charge light is solid and the first 50% green light blinks, and the other two green lights are off. As the battery charges then the first 50% blinking green light becomes solid and the next 80% green light starts blinking, and the third green light is still off. After fully charged to 100%, all green lights are now solid.
When the second battery is in bay #2 it will only have the single green charge light on, and the other three green lights are off. Then after battery #1 is charged, then battery #2 will start to charge, then it will follow the same process as battery #1 above.
When no batteries are in the charger, then no lights are on.
Also try another outlet in case there is an electrical short in the outlet.