Today, I changed the batteries in all my smoke detectors. I noticed that the battery light in one was blinking. Instead of only replacing the one with a new normal 9v battery, I ordered a pack of 10-year lithium 9v batteries and replaced them all. Now I don’t have to worry about changing them for a handful of years.
Edit - Funnily enough, dinner put them to the test. I was going to test them tomorrow when the kiddo is at daycare.
That would highly depend on the particular device and battery used. Electronics are designed to work within a voltage range because voltage often fluctuates, with both AC and DC. Some electronics can be more sensitive and require a more narrow voltage range or have a more stable range and some power sources can vary their range more and have a higher rate of fluctuation.