What makes one battery rechargeable and another not?
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There are two types of battery, primary batteries and secondary batteries.
The first are not rechargeable, they employ a chemical reaction that releases energy over time but isn’t reversible, once it’s discharged the reaction is complete and it’s not worth it to use electricity to reverse the reaction and obtain the original reagents.
The second type is rechargeable, their structure allows them to dispense energy through an electrochemical process, but that process is reversed easily by applying current to them, charging them once more.
They don’t use the same chemical reactions and materials.
The rechargeable battery can be compared to heating water : it boils and becomes a gas. When it cools down it becomes liquid again, just like when you recharge the battery you can use it again.
When you heat up an egg, it cooks and changes. If you let it cool down, it doesn’t revert to raw. Same as when a non rechargeable battery is used, its chemical compounds are used and cooked. Trying to recharge it won’t work (also don’t try, it can burn).
Technically most batteries are rechargeable, in the strictest sense of the word.
The batteries that are labels as rechargeable, use more expensive chemicals, that manage the heat of the recharge process such that the battery does not overheat.
The cheaper chemicals in a non-rechargeable battery, have no such consideration and can be very dangerous.
The chemicals inside it and the reactions that take place.
A battery runs on what’s called a galvanic cell; it converts chemical energy into electrical energy. This reaction is favourable or “spontaneous” as the chemicals want to react this way to get rid of some energy they have stored in them.
When you recharge your phone the cell flips to becoming an electrolytic cell. These favourable reactions are now being forced to undo themselves, giving the chemicals more energy, which they don’t want(so the reaction is now unfavourable and forced) – but they can then get rid of the energy again by powering your device.
In a non-rechargeable battery it is very difficult or impossible to make the reverse reaction happen.
To explain *why* a normal alkaline battery isn’t rechargable, it contains a small amount of water in it (despite being called a dry cell battery). If you connect it to a battery charger, it supplies enough voltage that the water inside the battery will split into hydrogen gas and oxygen gas (remember that water is H2O). Since the battery is a sealed metal cylinder, pressure builds up and can cause the battery to explode, catch fire, or leak.
Rechargeable batteries typically use a different liquid in them that doesn’t decompose into gasses like water does.
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