Testing batteries ensures they are charged and ready for use. Operating a device without knowing the batteries are charged means they may not function as expected, causing your device to fail to operate. Several simple methods are available to quickly test and determine if a battery is charged and functional.
Use a Multimeter
The most effective means of testing a battery is with a multimeter. You can test AA batteries and other battery types and styles with the device. The meter shows the voltage output, which indicates whether the battery is weak, dead or functioning normally. Not everyone has a multimeter handy, and other methods of testing are available for AA and AAA alkaline batteries.
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The familiar AA and AAA battery types are 1.5 volts, and the rechargeable versions are 1.25 volts. You might wonder at what voltage is a 1.5 V battery dead. If the battery tests at less than 1.3 volts in the multimeter, it no longer functions properly and should be replaced.
To run the test, set the multimeter to the DCV setting and set the voltage to 20 so it can read above the battery voltage. This simply places the reading capabilities in a safe range. Touch the black clip to the positive side and the red clip to the negative side of the battery to read the voltage. A reading of 1.3 to 1.5 volts means the battery is good.
A brand new battery might show a higher voltage level. Reading at 1.6 or slightly higher is not uncommon, and this is the reason for setting the DCV to a level of 20 volts as the maximum threshold.
The Drop Test
A voltmeter or multimeter is overkill for testing a few household batteries. If one is readily available, it makes sense to use it, but otherwise, a simple drop test can reveal the condition of alkaline batteries. The chemical composition in alkaline batteries shifts when the battery is dead, and the way a battery reacts when it is dropped reveals the charge status.
Hold the battery vertically, a few inches above a hard surface and drop the battery. A good battery lands with a solid sound and stands upright. A bad battery bounces and topples over. This test is simple and quickly determines which batteries are worth keeping.
Keep in mind that this test only works for alkaline batteries. Lithium battery types require a voltmeter or a device test to determine whether they are functional. The chemical composition does not change in lithium batteries, and the bounce test is irrelevant. However, alkaline batteries are far more common in the household.
Test in a Device
The device test is worth pursuing because the batteries must function well enough to power the device. This does not, however, reveal the charge for each individual battery because some devices can power with one weak battery and a few fully charged batteries.
Load up the device with batteries and test for power. If the device operates normally, run it until the batteries require replacement. Otherwise, replace them immediately. If the device continues to fail, the batteries may not be the problem. Test them in a different device to determine if the device has issues beyond the batteries. In some cases, cleaning the contacts resolves the issue.
While the device test is not foolproof, it is easy and convenient for any type of battery. The drop test for alkaline batteries is a better route for testing individual batteries, however.