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I tried a unviersal battery tester from Amazon, and it's already saving me money

This universal battery tester couldn't be easier to use, and is a great way to determine which ones are still good.

I generally use a multimeter, but that involves knowing what the voltages of a battery are when they're full and dead, so unless you have a brain that remembers stuff like that over people's birthdays, this isn't a practical method. The hardest part if figuring out which slot fits which battery, because if you get it wrong, it'll give you an inaccurate measure of how much power remains. Once you've figured out where your battery goes, push the positive end into the slot and use the probe to touch the other end (button cells slot into the tester in such a way that you don't need the probe), and the LCD screen will show you the voltage, remaining capacity, and a level bar display.

Get the Android app