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You probably know the feeling.

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Your phone utters 
its final plaintive "bleep"

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and cuts out in the middle of your call.

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In that moment, you may feel more
like throwing your battery across the room

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than singing its praises,

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but batteries are a triumph of science.

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They allow smartphones 
and other technologies to exist

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without anchoring us 
to an infernal tangle of power cables.

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Yet even the best batteries
will diminish daily,

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slowly losing capacity 
until they finally die.

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So why does this happen,

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and how do our batteries even store
so much charge in the first place?

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It all started in the 1780s
with two Italian scientists,

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Luigi Galvani and Alessandro Volta,

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and a frog.

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Legend has it that as Galvani
was studying a frog's leg,

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he brushed a metal instrument 
up against one of its nerves,

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making the leg muscles jerk.

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Galvani called this animal electricity,

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believing that a type of electricity
was stored in the very stuff of life.

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But Volta disagreed,

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arguing that it was the metal itself
that made the leg twitch.

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The debate was eventually settled
with Volta's groundbreaking experiment.

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He tested his idea with a stack
of alternating layers of zinc and copper,

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separated by paper or cloth
soaked in a salt water solution.

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What happened in Volta's cell is something
chemists now call oxidation and reduction.

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The zinc oxidizes,
which means it loses electrons,

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which are, in turn, gained by the ions in
the water in a process called reduction,

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producing hydrogen gas.

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Volta would have been shocked 
to learn that last bit.

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He thought the reaction 
was happening in the copper,

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rather than the solution.

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None the less, 
we honor Volta's discovery today

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by naming our standard unit 
of electric potential "the volt."

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This oxidation-reduction cycle creates
a flow of electrons between two substances

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and if you hook a lightbulb 
or vacuum cleaner up between the two,

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you'll give it power.

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Since the 1700s, scientists have improved
on Volta's design.

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They've replaced the chemical solution
with dry cells filled with chemical paste,

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but the principle is the same.

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A metal oxidizes, 
sending electrons to do some work

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before they are regained 
by a substance being reduced.

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But any battery has a finite 
supply of metal,

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and once most of it has oxidized, 
the battery dies.

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So rechargeable batteries give us 
a temporary solution to this problem

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by making the oxidation-reduction 
process reversible.

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Electrons can flow back 
in the opposite direction

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with the application of electricity.

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Plugging in a charger draws 
the electricity from a wall outlet

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that drives the reaction 
to regenerate the metal,

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making more electrons available 
for oxidation the next time you need them.

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But even rechargeable batteries 
don't last forever.

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Over time, the repetition of this process
causes imperfections

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and irregularities in the metal's surface
that prevent it from oxidizing properly.

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The electrons are no longer available
to flow through a circuit

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and the battery dies.

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Some everyday rechargeable batteries

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will die after only hundreds 
of discharge-recharge cycles,

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while newer, advanced batteries
can survive and function for thousands.

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Batteries of the future 
may be light, thin sheets

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that operate on the principles 
of quantum physics

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and last for hundreds 
of thousands of charge cycles.

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But until scientists find a way 
to take advantage of motion

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to recharge your cell battery,
like cars do,

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or fit solar panels 
somewhere on your device,

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plugging your charger into the wall,

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rather than expending 
one battery to charge another

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is your best bet to forestall 
that fatal "bleep."