Try moving the one on the left to the slot on the right and then inserting the other one. I have some snobbish trustfires that will only charge in certain slots. Don't know why but this works for me sometimes.
This. I have had the same thing happen. I also have two chargers and sometimes swapping chargers works as well.
Otherwise there is a possibility that you have a dead battery. If it continues to only show green, and you put both that one and its charged buddy into your lightsaber and it doesn't power up there's a good chance its dead.