I've got a few basses packed away that I don't want to dig out, and they have batteries in them. Someone told me recently that they don't leak and I don't have to worry about it.

True or False?

They can leak, I've seen it happen. I'd remove any that you think might stay in storage for like a year or more.

Leak as in leak their chemical content (as opposed to charge)? Batteries are generally full of powder rather than liquid, so are unlikely to leak. The Duracell safety information sheet for their 9v batteries is here

http://www.duracell.com/oem/safety/pdf/2027_2.pdf

That powder can distribute itself from the inside of the battery to the outside of the battery, leaving stains and damage. It resembles toothpaste IME- chalky and spreadable.

Side note - 9V batteries actually have 6 AAAA batteries internally.

If you have Duracells or something equivalent, not likely a problem. But you'll see reports on the web from people that had them leak anyway.

If the batteries are cheapies (or cheapies masquerading as expensive batteries), pull 'em. I had a bunch of Sharper Image batteries leak all over my TV/DVD converters. In the past I've had 9V batteries leak in pedals.

The likelihood is low, but....

js

Two years ago I had a Duracell AA leak into a multimeter and ruin it.

not a risk worth taking, if it were me. I've seen 9v batteries leak, and it's not a nice sight.

I'd have to agree. Be on the safe side and simply remove them. Then you know for sure you'll avoid any problems.

The battieres in my GF's vibrator leaked, & she now has a lingering acidic taste! :p

I've always used good quality 9V batteries but still couple of them leaked. Play safe and remove, if not in use for a long time

just replace them every year and you will be fine

Actually, when the grey gooish stuff comes out, its called "venting". I think its actually a safety measure somehow.