Batteries always seem to know the perfect time to frustrate you and run-out of juice. Whether it’s for your TV remote or your phone, having a full charge is always a relief. The difficult part, however, is when you can’t see the battery percentages on disposable ones. With this hack you can test out those batteries you found lying in your drawer!

Bouncing your batteries lets you know if you have an old dud or fresh charge!

The best method to “officially” test batteries is always going to be a multimeter. If you happen to have one of these lying around, simply place each end of the multimeter on the positive and negative terminals. For AA batteries, anything over 1.5 Volts is good. BUT WAIT.

You probably don’t have a multimeter or you wouldn’t be here right now.

Unless you are an electrician or handyman, you have no reason to keep a multimeter around. If that is you, there is a hack that lets you see if your battery is fresh.

The bounce test!

All you have to do is take two alkaline batteries, one old and one new, and bounce them on a hard surface. Take one of them in your hand, hold it two inches or so above the surface with the flat side facing down, and drop it. The fresh battery will land with a dull thud and bounce very little, if at all. The old battery will bounce much higher and will probably fall over.

The bounce test can tell you if a battery is fresh, but it can’t tell you the charge.

Don’t go throwing away your bouncing batteries yet! While this test is useful, it isn’t foolproof. After about 50% charge the batteries don’t see much change in “bounciness”. This means that a battery that bounces could be old, but not fully spent.

Why does this work?

In order to understand the reason behind the bouncing battery test, you need to learn a little bit about how batteries work! A study done by Princeton University provided some details into the process.

“Electricity is generated by a chemical reaction inside the batteries as zinc changes to zinc oxide. Initially, a layer of zinc surrounds a brass core in the battery like a donut around a hole. As the battery discharges, the zinc donut gradually changes to zinc oxide.”

This means that as the battery uses power, the zinc metal inside gets slowly turned into a “harder” version of itself. Harder things are typically bouncier.

“The zinc oxide begins to form on the outside and it pushes its way to the core,” Steingart said. “As you get more and more zinc oxide, and the zinc oxide begins to appear everywhere in the zinc layer, the battery gets bouncier and bouncier.”

As the battery continues to be used, more of the zinc gets turned into the “harder” version of itself.

Zinc oxide is what they use in golf-balls to make them fly further! At a certain point, however, the battery hits beak bounciness. After about 50% the battery bounces to the same height as a completely dead battery.

“But the formation of the bridges reaches a maximum “bounce level” well before the oxidation of the zinc is complete. That means that the bounce will reach a peak and level off well before the battery is dead.”

Check out the video below for an example of the bounce trick!

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Source: Princeton, Home Hacks