1) Plug the black test lead into the COM jack at the bottom of the multimeter.
2) Plug the red test lead into the “BATT uA mA” jack, right next to (left of) the COM jack.
3) Press the ON/OFF button of the multimeter to turn it on.
4) Set the the rotary switch to “1.5V” (that’s one of the three battery test settings, 9V, 3V, and 1.5V)
5) Using the test leads, touch the tip of the black test lead to the negative pole of the AA or AAA battery, and touch the tip of the red test lead to the positive pole of the AA or AAA battery.
6) Read the voltage displayed on the LCD display of the meter. It will tell you the voltage of the AA or AAA battery “under load”. Under load means that the meter is closing the circuit and draws a small current out of the battery, which makes it behave as if it was in use. This is a more accurate test than simply measuring the voltage without placing it under load, in which case the voltage will often be higher and misleading.
7) Now that you know what voltage the AA or AAA battery produces under load, you can use that information to determine how much battery life you have left, approximately. Simple battery testers usually give you a “green/orange/red” test result. The multimeter you bought gives you an accurate voltage reading instead, but you have to know what it means. A full new AA or AAA battery measures 1.55..1.65V. A used battery that still has some usable juice left will read between 1.25V and 1.55V. If the reading is below 1.25V the battery is typically more than half empty, and below 1.1V it’s pretty much done and not worth keeping it. Time to recyle. Under most conditions, the discharge of the battery between 1.5V and 1.0V is pretty much linear, so if it’s at 1.25V you can assume you got about 50% left. But true remaining battery life depends on many other factors, such as age of battery, temperature, load current, and battery brand.