Learn how to test a battery. Learn how to test a battery. How to use a multimeter to test a battery. What happens to the battery voltage under load. How to tell if the battery needs replacing.
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To measure the voltage, we simply need to select the DC function on our multimeter, and then we connect the red lead to the positive terminal and the black lead to the negative. This will give us a voltage reading. You can see that this battery is rated at 1.5 volts, but when we test it, we get 1.593 volts. The two values are close, but usually not the same.
When the battery is dead or dying, we get a lower voltage. This one, for example, reads 1.07 volts, so it’s completely dead. However, sometimes we could still get a voltage of around1.5 volts. Even if the battery is of no use. To fully test the battery, we need to test it under a load condition to check whether it’s still useful. And for that we need a resistor.
So we take a resistor of around 100. Ohms, but it doesn’t have to be exactly this value, though. We connect the resistor between our two probes. In this case, I’ve just used some crocodile clips to connect the resistor between the probes like this. This way current will flow through the resistor and we can take a voltage reading as this occurs.
If the battery is still good, then the voltage level will only drop slightly. For example, this battery has a rated voltage of 1.5 volts. With no load. It is 1.593 volts.
With the resistor connected, we take a reading of 1.547 volts, so this battery is still good. However, this battery is also rated at 1.5 volts. When we take a measurement with no load, it oddly has a reading of exactly 1.5 volts. But when we connect the resistor, we can see that the voltage has dropped to 0.863 volts. So we know that this battery has run out of charge.