Of course, a flashlight is an appliance for storing dead batteries.
And since you brought that up - Dig through all your little nooks, crannies, and sock drawer and to everything you've forgotten about or haven't used in years. Pedals, recorders, flashlights, cable tester, multimeter . . whatever. Open the battery compartment and if there are batteries in there, remove them. Hopefully you can.
One of the problems with alkaline batteries and some low-current (or little used) devices is that the batteries operate for so long that you forget about them, and then they leak. If you catch a leaky cell early enough, you can clean up the corrosion with a cotton swab and water, but if they're pretty far gone, chances are pretty good that the electrolyte has begun to attack the metal parts of the battery holder, or worse, has gotten into the works and is eating away at circuit board traces. It may be difficult to salvage.
Small electrolytic capacitors can also leak, and they're mounted directly on the circuit board so they start eating the traces pretty quickly. I had that happen in the passive crossover network of one of my KEF monitor speakers - it ate through a circuit board track which caused the tweeter to be intermittent for a while, then quit completely. After I found the problem, I checked the other speaker and, sure enough, the same capacitor in that one had become leaky, too. Another thing I had here that took me a couple of years to find, was my non-working MIDI guitar. After replacing all of the electrolytics when discovering that most of them had started to leak, and that didn't solve the problem, I eventually found an etched-through circuit board trace. That took me about two years of intermittent (me, not the problem) troubleshooting.