Watch the display for your voltage reading. Before you learn how to test a car battery, there are a couple of things to keep in mind. A multimeter itself is going to test one thing on the battery, and that’s to measure voltage. A battery test at AutoZone has an advantage in that it’s going to simulate a starting load on a battery.
When testing the battery under a heavy load, switch the meter to the 20-volt DC range. If you don’t have a high-load tester, use a 100-watt light bulb as a substitute. A 100-watt bulb draws about 8 amps from the battery when on and about 1 amp when off.
Voltage essentially tells you how “full” the battery is at that moment. Steps to Check Voltage: Set your multimeter to DC voltage mode. Look for a “V” symbol with a straight line on your multimeter’s dial. Adjust the range slightly higher than the battery’s nominal voltage. For example, set it to 10V if you’re testing a 3.7V battery.
You can use a hydrometer-style battery tester to test the individual cells by testing the specific gravity of the acid in each cell, but even once you find a bad cell, you’re arriving at the same place you would by simply using your multimeter to do some simple voltage tests.
Monitor and record the discharge time. Connect the battery in series with the multimeter to measure the current drawn by the load. Calculate the capacity by multiplying the discharge current (in amps) by the time it took for the battery to reach its cutoff voltage.
Connect the probes: Place the red probe on the positive terminal and the black probe on the negative terminal. Read the voltage displayed on the screen. Interpreting the Voltage: A fully charged lithium battery (3.7V) should read between 4.1 and 4.2 volts when fully charged.
In order to test a battery, the tester places the battery under a load. Each battery has a rated load. If the test comes back and says the battery can''t support the load, it''s a fail. If it can, it''s a pass. However, if a battery is marginal, it''s …