Thanks for that Tets. I saw those two screws there, but didn't think that was the battery cover, as all other battery covers only had one screw.
Since it has the bigger batteries, I'll get to mine straight away. Like you, mine still makes the noise, but those bigger batteries leak faster than the button cells.

As for resurrecting the electronics by cleaning up the contacts - it's good to hear, but I fear I may not ever have the time to do that with all the ones that no longer work... especially if it is a gimmick that I'm not likely to ever need again.
I like showing off the gimmicks to others, but it isn't worth having batteries in them all the time to do that, because the way they have battery covers screwed down it is too time consuming to be able to just put them in when needed.
(Gen1 toys were great, with battery covers that could just unclip and easily re-attach quickly)