Hmmmm .... I never throw away a flashlight battery .... whether it be carbon or lithium .... until I've checked it's voltage with a four-place meter. I save throwing away a lot of batteries before their time. Many other things can be "wrong" with DC systems that may make it appear that their batteries are bad/low when that's not actually the case -> no current measurements required.
However, in our RV I do watch coach battery amperage draw when near the end of charging to tell when they're full for their age -> amperage drops to zero when they're full .... regardless of whether or not they can still take in their original as-new amp hours.
