I've fixed the issue, so this might not be the right place for this question. If so, apologies.
Question: Am I right that the 4x9v batteries in one compartment run the LEDs, and the single 9v in the other compartment runs the bass electronics??
Here's why the question: My SC short scale deluxe started buzzing this afternoon - the low battery kind of buzz. I changed the batch of four in the large compartment, same problem. Then changed the single battery. Fixed. So I'm guessing that it's the single battery that runs the electronics, the flip of what I'd originally thought.
(Yeah, should have started with switching out the single, although better to change all at once, I think.)
In any case, all's well, and it's a joy to play!