Ever spent ages swapping batteries in and out of remote controls to find out which ones still have power in them?
Next time, just try dropping them on a hard surface and see if they bounce.

This is because spent alkaline batteries are more likely to bounce than fresh ones, according to an American electrical engineer whose video demonstrating the phenomenon is becoming an internet sensation.

To test outgassing, Mr Hite dropped a weight on the battery. If there was a build up of pressure, a weight should bounce higher on one than the other. He also drilled holes in the batteries to release this pressure. There was not a 'convincing' difference in the first test, and the bad battery still bounced in the second

In his YouTube video, Lee Hite tests a series of batteries that have expired against a set which have not been used.
He demonstrates that a used battery bounces far higher than one that has only just been taken out of the packet.
在视频中,电气工程师Lee Hite测试了一系列用完了的电池和刚拆开包装的新电池。

A good battery, he explains, contains a gel-like substance which solidifies as the battery discharges its electricity.
While the gel is in a semi-liquid form, it absorbs the energy when the battery hits the surface.

An anti-bounce hammer, which contains an internal core of moving buckshot, works in the same way.
When the gel in the battery has solidified it cannot move and the whole battery bounces, the same way that a solid hammer bounces off a nail.

The theory was greeted with caution by academics in Britain last night, as chemistry and physics departments across the country tried to test the idea for themselves.
Many said the theory made sense – but few were able to replicate Mr Hite's results.
A spokesman for the Institute of Physics said there was 'sound thinking behind the idea' but added: 'Experiments need to be reproducible for results to be reliable. We're struggling to replicate the experiment over here.'

In terms of the anti-bounce theory, Mr Hite used hammers to demonstrate. A regular hammer will bounce when hit against a surface, but an anti-bounce hammer (pictured) is fitted with buckshot. As the hammer hits the surface, the buckshot lags behind, and when the hammer hits the base, the buckshot catches up with it

Dr Lee Banting, a senior lecturer in chemistry at the University of Portsmouth, said the video had convinced him. 'If the gel in the battery is in a liquid state it absorbs that kinetic energy – all the energy is gone and the battery does not bounce back,' he said.
'But if it turns into a solid state the kinetic energy pushes it back away from the surface and it bounces.'
朴茨茅斯大学的Lee Banting说该视频很有说服力。如果电池中的凝胶状物质处于液态,那么它会吸收电池下降的动能。电池没有了动能自然无法弹跳起来。而固态的凝胶状物质无法吸收动能,电池有了能量是会被坚硬的表面反弹起来。

Mr Hite then 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

Dr Fred Davis, a chemist at the University of Reading, said: 'This video has prompted me and my colleagues to dig out dud batteries from all over the place to try it out for ourselves.'
He added: 'The energy output of a battery arises from chemical changes, which means the material in the battery at the start will be chemically different from that when discharged.
'It may be that these changes would influence how it behaves when dropped on to a desk. But I remain to be convinced.'
不过也有学者持不同观点。英国雷丁大学的化学家Fred Davis教授说:「看了这段视频,我和我的同事们找出了所有的废电池。电池依赖化学反应放电,这意味着新电池与废电池中的化学成分不同。也许这些化学变化会影响它们掉落在桌上的反应。」

A spokesman for battery maker Duracell said: 'This bounce test is certainly not an accurate way to measure battery life.'
He added: 'While the density of the materials does change as the battery is discharged, it is not indicative to power delivery.
'As batteries are discharged, the internal volume increases due to the expansion of materials. This often makes the battery swell and can play an important role in how it will balance when dropped.'

本文翻译自:Want to know if a battery is dead? See if it BOUNCES: Engineer claims simple trick reveals if a cell has lost its charge


When you bounce a dead, or bad, alkaline battery on a solid surface it bounces, while a good battery falls over (pictured). Electrical engineer Lee Hite has created a video to test two theories - outgassing and the anti-bounce theory - to explain why this phenomenon occurs