but wouldn't the sound not work if the batteries weren't charged.. i get sound from it just no light.. or does the led run off a different battery??
No, both Li-ONs total 7.4V and are needed to power the Obsidian and buck puck. Question: did both batteries charge and finish at the same time? I wonder if a dead cell is allowing the Obsidian to work, but not enough to power the MLS.
Did you get quick disconnects with the MLS? It's a very long shot as the QDs stay together tightly, but maybe verify if the QDs are connected properly?