We have an Energizer [url=http://data.energizer.com/PDFs/chdc7.pdf] (PDF data sheet). It’s worked problem-free for a few years, and the only batteries we’ve ever put in it are Energizer branded batteries sold with/along side the unit.
Recently, we noticed that it will occasionally act a bit contemptuously—it’s started making electronic spitting noises. Not quite an electric crackle, much more as if one of the batteries is off-gassing (maybe it’s not contemptuous as much as flatulent). The noises are short bursts, one or two at a time, then nothing. I don’t know if they repeat, because we’ve unplugged the unit right away.
The charger itself is an easy replacement (if that’s where the problem is). If it’s a battery that went bad, is there any way to test which one it is?
Any ideas what’s happening? Is it dangerous? Who am I kidding—any plug-in device that begins making unauthorized noises is, generally speaking, a threat to all of humanity.
I’m inclined to think that you need new batteries if you are still using the original batteries after several years; they don’t last forever, especially if they are frequently used. You should also never mix old and new batteries, rechargeable as well as non-rechargeable (due to capacity differences, rechargeable batteries lose capacity over time; newer batteries often have a higher mAh (capacity) rating as well due to improvements), so they should all be replaced at the same time.
I eventually contacted them directly, taking a minute to copy the OP into their customer support email. They responded quickly, telling me to ship them the batteries for inspection/replacement per their guarantee (they even included a prepaid mailer).