The photo shows an inexpensive (often free) multimeter from Harbor Freight. I added a white dot to the indicator. Notice that the white dot points to a battery test function for 1.5 volt and 9 volt batteries.
Batteries should normally be tested under a load because a no load voltage test could read normal, but drop considerably when the battery is under load. This multimeter's manual indicates that the battery test circuit adds 360 ohms of resistance as a load. According to the label on the meter, a 1.5 volt battery in good condition should show a current draw of 4 milliamps or more and a good 9 volt battery should show a current draw of 25 milliamps or more. There is nothing mysterious about this. It is a simple application of Ohm's Law, which says that voltage (E) in a direct current circuit is equal to resistance (R) multiplied by current (I), or E = IR. Factored, that is current (I) equals voltage (E) divided by resistance (R).
Step 1: No battery test function on your meter
This is not my better meter, but one I needed in a second location. It does not have a battery test function, but I decided it would be handy to add one. I can use the 200 m function. But, I will need to add about 360 ohms in resistance when in use. (My better meter also does not have a battery test function, and I made one of these resistor probes for it, too.)