I have the GWB-1 and it has developed a problem of the battery not sitting snug in the compartment. This causes a lovely huge pop sound if I move the wrong way. I’ve had to wedge in a piece of sponge to keep this from happening. Is this a widespread problem with these basses?
Actually, it’s a problem with battery manufacturers. Here’s a couple of batteries I grabbed out of my recycling box:
Here’s another example from some battery experts.
Since the design of the battery holder in the GWB basses depends on the reasonably snug fit of the battery to hold it in place, the solution you’re using is necessary but it’s only a problem if you happen to buy a “short” 9-volt battery. Go ahead an use the foam but remember to compare battery sizes the next chance you get to shop for some.