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How does a battery tester work?

Shop for Battery Testers

battery disposal Battery testers are one of the electrical tools that can be used by anyone, as they do not deal with exposed sources or high levels of electricity. Additionally, there are no complicated measurements to interpret – the battery tester will simply tell you whether a battery is worth using or needs to be disposed/ replaced.
battery power A battery tester’s product spec should state that the device tests the ‘power’ remaining in batteries. This is not referring directly to the power as in the wattage, as battery testers work by testing current or voltage output.

How do the analogue and digital battery testers differ?

analogue and digital battery tester There are both analogue and digital battery testers available. They are used in similar ways, only the display is slightly different; the digital one using an LCD screen with bars as indicators and the analogue using a needle dial.
batteries in remote However, they work slightly differently: analogue battery testers measure batteries under load, which means they test the batteries as if they are in use. This gives a more accurate picture of the battery’s remaining life. See below for more information.
digital battery tester requires batteries Digital battery testers need a battery to function and do not include the resistor, which is what measures the battery under load on an analogue tester. Digital battery testers are not as effective as their analogue counterparts because of this.
How do you test the battery in the battery tester then?

The inner workings of an analogue battery tester

danger high voltage sign Battery testers rely on the voltage of the battery, which is the electrical potential difference between two points. Every battery will come with a voltage reading; for instance, a non-recyclable, alkaline AA battery has a voltage of 1.5v.

For a battery to be working at its best, the voltage should be at the value stated or slightly above. When it falls, the battery tester will indicate the battery is low or needs replacing.

For more information on electricity and voltage, see: Wonkee Donkee’s lesson on electricity and How can electricity be detected and tested

battery tester in use When a battery is inserted into the tester, it completes a circuit, which releases both the current and the voltage from the battery, allowing electricity to flow around the circuit in the battery tester. When electricity is flowing, the voltage and current are responsible for creating electromagnetic waves. The higher the voltage and current, the more electromagnetic waves are produced.
magnetic field coil A battery tester’s circuitry includes a wire coil which is suspended between two magnets. When the test battery is in circuit, the electromagnetic waves, created at the coil, act against the magnets’ charge and cause the needle to pivot. As the electromagnetic waves are dependent on current and voltage levels, the amount the needle moves is an indication of the levels remaining in the battery.
battery tester scale The scale on a battery tester does not indicate the actual levels being tested, however. It simply tells you whether a battery can still be used or whether it is too run down.

For more information on the scale, see: What are the parts of a battery tester?