In order to charge a cellphone (or any battery),
you need to provide a flow of charged particles
(current) with enough driving force (voltage).
A wall socket or USB port provides a steady
current at a standard voltage but any current with
enough voltage will charge your phone.
Certain fruits and vegetables can be a source of
charged particles, particularly squishy ones with
lots of minerals, salts or acids. Citrus fruits
like lemons or grapefruit work best, but you can
use potatoes too. Watermelons could work but
don’t have as many minerals/salts/acids as a
lemon, despite being a bigger fruit.
Charged particles on their own are not enough –
which is why your phone doesn’t charge if you plug
it directly into a lemon. There’s no driving force
(voltage) for the charged particles to flow into
and out of phone. One way to apply voltage is to
use two different metals to connect your phone to
the fruit. For example, the difference in energy
between copper and zinc will create a voltage of
~1.1V, a little less than a AA battery. When stuck
into a fruit, the charged particles move away from
the zinc and toward the copper, which causes
electrons from the copper to pass through your
phone to the zinc. This flow of electrons
(current) has enough driving force to
charge your phone.
Any YouTube video that claims you can charge your
phone using only a cold watermelon is a
fake, but fruit-based batteries are real. The
secret isn't the choice of fruit – it’s the choice
of metals you use to make the connection.
For more information, check out this video:
If you’d like to try making fruit batteries at
home, check out this website:
I have to answer this in two parts: the
watermelon battery itself and some practical
The first part is about the watermelon itself.
Yes, it is possible to draw electrical power
through a watermelon by turning it into a battery.
To make a battery, we need to put two metal
electrodes inside an electrolyte
(battery acid), then connect the electrodes by a
conductive wire. For example, one of the
electrodes can be zinc (like on a galvanized nail)
and the other can be copper (like a penny). The
watermelon provides the electrolyte, watermelon
The electrical power that this battery
generates does not actually come from the
watermelon. Instead, it comes from a pair of
chemical reactions that happen when all of the
battery parts are connected, called reduction and
oxidation (or together, redox, for short). In our
example, the oxidation reaction pulls two
electrons off of a zinc atom, causing zinc ions to
dissolve in the watermelon juice. The reduction
reaction takes the electrons and combines them
with two hydrogen ions from the juice to make
hydrogen gas. Together, these two reactions move
electrons from the zinc electrode through the wire
to the copper electrode, making electricity.
Now for the second part, the practical
concerns. You might not be surprised to hear that
commercial batteries are much more powerful than
watermelon batteries. They use better combinations
of electrodes and electrolyte to generate much
more electricity. To get enough power for your
iPhone to even detect, you would probably need a
few watermelon batteries linked together in
series. Finally, there is the question of what the
iPhone itself will do when it detects the
watermelon battery. If the power source is not
a good match, the phone might be able to block it
to protect itself.
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