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How to convert an AA battery to a D battery

How to convert an AA battery to a D battery
In case of emergency, you can make D batteries by converting AA batteries.
Do not panic when D batteries are out of stock. Your AA batteries will do.

 - <How to make a D battery from an AA battery (1)>
See the diagram above. Place a metal ball (like a "pachinko ball") either on or under an AA battery. Wrap a piece of paper around it to fix the ball. Voila! Now you have a D battery. The diameter of a "pachinko ball" is smaller than that of an AA battery; fix the ball tightly with scotch tape. Or you can wrap another piece of paper around the ball to adjust the size. For easier replacement of the battery, the latter option is recommended.

 - <How to make a D battery from an AA battery (2)>
Instead of metal pachinko balls, you can also use 1-yen coins (which probably are easier to find). Take eight 1-yen coins. You can also use 8 of 10-yen coins (though it costs 10 times more!). Both coins are 1.5mm thick, so 8 of these coins will make 12mm thickness. If your battery case is a little tight, take 1 coin out to adjust the length to get 10.5mm thickness.

WARNING: For your safety, DO NOT mix 1-yen coins and 10-yen coins.

 - Tape 8 (or 7) coins together to make a cylindrical form with 20mm in diameter and 12mm in height. The diameter is a bit bigger than that of an AA battery. Wrap a piece of A4 paper around the AA battery to adjust the size. Place the coins under the battery. Wrap another A4 piece of paper around them (after folding it in four as shown below). The width of the folded piece is a little narrower than that of a battery, but no worries! 5 pieces of A4 paper would be sufficient. 

 - <How to make a D battery from an AA battery (3)>
Some people tweet that they use tinfoil. It's actually a good idea, quite easy to find materials (most of you have tinfoil in the kitchen) and to make batteries. But I have yet to know the information on the adequate amount of tinfoil as I myself haven't tried this method.

 - The overall process is similar to (1), but this one is easier.
The tinfoil needs to be solid to retain the electrical contact.Place the tinfoil ball under the AA battery and wrap pieces of paper around them (see a diagram above). Again, A4 paper is recommended, and 5 

Above are 3 easy ways to make a D battery from an AA battery.
 - Although such DIY batteries are NOT for everyday use, the skill (even elementary school kids can do!) enables you to use radios and flashlights in disaster areas. It may also help you stay calm and survive in emergency situations. 

 - Photos below are the batteries I actually made.
From left:DIY D battery, ordinary D battery, DIY C battery and ordinary C battery. 

 - D battery by method (2). Note that there are two layers of the wrapping paper.
Paper width should be a bit narrower than the battery itself to avoid possible failure in connection.

 - Why shouldn't we mix 1-yen and 10-yen coins together?
Those coins are made of different metals. Using different metals at the same time may cause trouble to the electric current and damage the coins. You may violate a law if the coins are transformed by damage.

 - Does this violate Act on Control of Damaging and Other Acts Related to Coins?
No. In Japan, there is a law called "Act on Control of Damaging and Other Acts Related to Coins", which prohibits reshaping bills and coins such as melting and scratching. Also, forging bills and coins is strictly forbidden.

 - The capacity and the electromotive force of a battery is predetermined. Secondary batteries, such as Eneloop, are better for a long period of use than alkaline or manganese batteries.

 - If you don't have paper
Try using cardboards or other paper materials instead.

 - If you don't have any tapes
You can use tapes, strings, straps, papers and any other materials as far as it fixes the battery properly. You can also use some rice as glue.

 - You could make 11-yen battery; you can find the link for instructions (see Japanese website for details).