I'm testing old 12v batteries. I'm using a load tester and a multimedia. I'm confused as to why the load tester is measuring a different voltage than the multimeter. Without any load on it. Is on one battery for instance the multimeter reads 12.83. And the Is load tester reads 6v. I'm completely new to this and any advice would be much appreciated.

 

I'm testing old 12v batteries. I'm using a load tester and a multimedia. I'm confused as to why the load tester is measuring a different voltage than the multimeter. Without any load on it. Is on one battery for instance the multimeter reads 12.83. And the Is load tester reads 6v. I'm completely new to this and any advice would be much appreciated.

Load tester measures the battery voltage under given load conditions, so the measured voltage is a EMF - Rint*Iload=EMF - Rint*EMF/(Rint+Rload). The voltmeter measures the unloaded battery voltage = approximately EMF (the voltmeter input resistance Rint is very high).

 

Batteries will not show their correct voltage unless they are under a load. If you simply take a multimeter (or battery tester) and connect the leads to each battery terminal, you will not get an accurate reading.

Expensive, high-end and specialised battery testers are designed to place the battery under a load in order to get an accurate reading, while multimeters provide a guide as to the voltage potential.

When testing batteries with a multimeter, you must have the meter set to measure DC voltage and place the battery under load by using a resistor in parallel with the test leads of the meter. A battery can be used until it is down to about 30% capacity. After that, it typically will not supply enough voltage to power the product it is being used in. The actual cut-off voltage will vary with the battery type.

 

Load tester is used in measuring the battery voltage under given load conditions.

Whereas multimeter measures battery voltage and helps gauge the battery's health. By setting a multimeter to DC volts and connecting it to the positive and negative terminals of a battery, the multimeter will measure its voltage.

You can find out more about using multimeters here: https://www.theengineeringprojects.com/2022/08/how-to-use-a-multimeter-on-a-car.html

 

Batteries will not show their correct voltage unless they are under a load. If you simply take a multimeter (or battery tester) and connect the leads to each battery terminal, you will not get an accurate reading.

Expensive, high-end and specialised battery testers are designed to place the battery under a load in order to get an accurate reading, while multimeters provide a guide as to the voltage potential.

When testing batteries with a multimeter, you must have the meter set to measure DC voltage and place the battery under load by using a resistor in parallel with the test leads of the meter. A battery can be used until it is down to about 30% capacity. After that, it typically will not supply enough voltage to power the product it is being used in. The actual cut-off voltage will vary with the battery type.

What is the ohm rating for resistor are you referring to for testing battery load ?