This has happened on my Celestron 4" astronomical telescope, not a light-generating but rather a light-gathering device, if you will, and more expensive than any flashlight I ever hope to own. I hadn't had the thing out of the closet for quite a while and then, glimpsing its case on the shelf, had an awful feeling (call it a loving father's instinct)- and sure enough, two of the four alkaline AAs on the motor drive had leaked, corroding and blackening the terminals [if perchance you don't know, the motor drive in the base of such a scope turns it and keeps the scope focused on the same spot in the sky, otherwise the view moves as the earth turns, making the motor drive VERY handy). Normally, with alkaline batteries, I clean the corrosion off and swab with vinegar (the anti-alkaline!) to stop further damage, then polish the damaged metal and test. But I haven't tested the 'scope with new batteries because I'm afraid I won't like the result... or the hundred dollar repair job. Does anyone have any advanced tips on repairing such battery terminal damage?