Probably time for NiMH batteries, but maybe not just yet in this application. The batteries were installed (new) just a few weeks ago. It was in a remote and I heard it just pop last night. Thought it might be an electrolytic cap in the remote, but it was still working. At least until this morning when I tried it and it wasn't powering anything. I used a couple of NiMH batteries I had (from another device) and the remote was still working. Then I took a battery tester to the batteries, where one looked show almost new voltage while the other was well in the "replace" area. It doesn't display voltage, so it's pretty crude. But clearly one of the batteries just had a sudden failure and probably that sound was the result. It's showing a lower reading than the batteries that I replaced when there was a low battery warning from the device (which communicates with the remote).