What is best way to test a dry cell battery(C, D, AA, AAA, etc.) with a multimeter? I don't think voltage is.

Voltage is the correct way. A battery in new condition will have 1.5 volts or a bit more; end of life depends on the device, but anything under 1.2 volts is probably grounds for replacement.

What is best way to test a dry cell battery(C, D, AA, AAA, etc.) with a multimeter? I don't think voltage is.
Since the power output vs voltage tends to be predicatble it is a pretty good way. Better would be to put some small load on it and measure voltage while driving a load, as that will actually give you a power output. I suggest a resistor with a value of roughly 100Ω. This will give a good indication if the battery produces voltage but can't produce any power.





You'd have to make up a lookup table to get you the ability to predict remaining power/time per charge.
Reply:Measuring the voltage probably isn't the best way, because it is the battery's internal resistance which goes up (leaving relatively little voltage to be dropped across low impedance external devices) rather than the voltage which goes down. Measure the current.