Tangledwood - that's a dreaded outcome..

I know I still have at least 2 active pickup guitars with 9v Batteries in them,
that I've not been able get out of storage for several years...

But so far I've been lucky with 9v's..
Last year I set a day aside, to take out all the 9v Batteries of any devices I owned.
Or at least most of 'em..

Some of these batteries had been installed for many years, forgotten about.

Fortunately I only found one that had started bulging at one end,
but not yet leaking..

Mudcat Techies might explain to us why 9v batteries seem to be less likely to leak...???