In sci.electronics.repair, Phil Allison wrote:
What else are are high capacity , rechargeable 9V batts good for?

Maybe he's got an old transistor radio. I've got a portable tape player
(not cassette, it's open reel) that uses I think two or four C cells for
the motors and a 9V for the "brains".

I gather that there are a bunch of small electronics projects that use
nine volt batteries, too. Arduino 9V battery connectors are something
I've seen for sale a number of times.

Elijah
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has no personal experience using an Arduino 9V battery connector