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A YouTube video last year had us all bouncing our batteries to determine whether or not they still contained charge. 

But despite initial claims that a bouncy battery is 'dead' and should be thrown away, scientists have discovered this isn't exactly the case.

Using a combination of X-rays and lab experiments, engineers confirmed batteries do indeed bounce as they lose charge - but the highest bounce occurs when the battery is half full. 

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Using a combination of X-rays and lab experiments, engineers confirmed batteries bounce as they lose charge due to zinc oxidisation. But, the 'maximum bounce' occurs when the battery is around half full (shown) meaning the test doesn't tell you if a battery is dead, it just tells you whether the battery is fresh 

'The bounce does not tell you whether the battery is dead or not, it just tells you whether the battery is fresh,' said Daniel Steingart, an assistant professor of mechanical and aerospace engineering and the Andlinger Center for Energy and the Environment from Princeton University. 

The battery bounce test became popular when Cincinnati-based electrical engineer Lee Hite posted a video demonstrating the theory.

In Mr Hite's tests, he dropped 'good' and 'bad' batteries - charged and empty - through a tube to test their bounciness before opening them to discover how they differed inside. 

He conclude that good batteries don't bounce because of the anti-bounce theory. 

This theory states the gel-like substance in a good battery creates a downward force, keeping it flush with the floor when dropped.

Professor Steingart, along with his colleague Shoham Bhadra, were inspired by this, and similar videos, to put these claims to the test. 

Electricity is generated by a chemical reaction as zinc changes to zinc oxide. Zinc starts out as a packed bed of particles that move past each other. But as the zinc is oxidised it creates bridges between these particles, causing the inside of the battery to resemble a network of 'springs'. This is what gives the battery its bounce

The height of the bounce increases as the batteries discharge, and this has led to the common conclusion that internal changes related to the reduction in charge cause of the higher bounce.

But Professor Steingart was intrigued by this discharging, because it is not linear.

Instead, the height rapidly increases and then levels off - a discovery Professor Steingart and his team had made previously in their work into the internal changes related to battery discharge. 

So they dropped batteries through plexiglass tubes, and used a computer microphone to record them striking a benchtop. The researchers were then able to use the time between bounces to determine the height of the bounce.

The team then combined this data with X-ray scans of batteries that had been taken by researchers at Brookhaven National Laboratory.

This revealed the bounce was caused by the way the batteries produce power.

Electricity is generated by a chemical reaction inside the batteries as zinc changes to zinc oxide. 

To begin with, a layer of zinc surrounds a brass core in the battery, which the researchers compared to being like a 'donut around a hole'. 

As the battery discharges, the zinc 'donut' gradually changes to zinc oxide.

'The zinc oxide begins to form on the outside and it pushes its way to the core,' Professor Steingart said. 

Cincinnati-based electrical engineer Lee Hite posted a video (pictured) showing bouncing batteries. In his tests he dropped 'good' and 'bad' through a tube to test their  bounciness before opening them to discover how they differed inside. He conclude that good batteries don't bounce because of the anti-bounce theory 

Mr Hite cut the batteries open to see how the electrolyte in a good and bad battery differs. In a good battery, it has a gel-like substance (left), while in a bad battery it is solid (right). Mr Hite believes the gel in a good battery works in a similar way to the buckshot in the anti-bounce hammer and causes a downward force

'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.'

He continued that the zinc starts out as a packed bed of particles that move past each other. 

But as the zinc is oxidised it creates bridges between these particles, causing the inside of the battery to more closely resemble a network of 'springs'. 

This is what gives the battery its bounce.

However, the number of these bridges peak before the oxidation of the zinc is complete, meaning they reach a maximum 'bounce level' as the battery loses around 50 per cent of its charge. 

From this point on the battery bounces to a similar level until it is 'dead'.

The findings are published in the Journal of Materials Chemistry A.  

Other researchers involved in the project included Benjamin Hertzberg and Andrew Hsieh, from Princeton, Mark Croft from Rutgers University;,Joshua Gallaway from City University of New York, Barry Van Tassell from the City College of New York,  Mylad Chamoun, Can Erdonmez and Zhong Zhong from Brookhaven National Laboratory and Tal Sholklapper of Voltaiq.