Eli5: Why are all batteries not rechargeable and what causes batteries to become rechargeable?

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Different batteries can use different chemical processes to produce energy, and some of those processes are more easily reversible than others. Imagine one as lighting a fire to make some heat and another as raising a heavy stone to turn a wheel. It’s much easier to turn the wheel back after the stone has fallen down, but not so easy to unburn a coal. We choose different processes to produce energy in different situations depending on what stuff we have available on Earth and what produces the kind of energy we need in different situations.


It has to do with the construction/design of the battery, non rechargeable ones are simpler to create, but they don’t have the pathway to reverse the reaction and recharge the batteries. Simply put, batteries are a chemical reaction that uses the flow of ions to create an electric current. How this happens essentially is this: an electron leaves the anode, traveling along a wire to the cathode, at the same time a positive ion is released from the anode, so it loses on negative charge and one positive charge. On the cathode side of the battery, the electron that traveled to it meets with different kind of positive ion and combined with it to make a neutral charge. This flow of ions is crucial to absorb the electrons in the cathode because other wise the cathode would build up a negative charge and no more electrons would be drawn to it and your battery is dead. So in this process, we essentially have the anode losing material, and the cathode building up material. When we charge a battery, use electricity for force this reaction backwards, causing the cathode to release ions and the anode to regain the ions it lost. Not all batteries can do this because you need some sort of solution or pathway that lets the ions travel in the opposite direction. This is also why rechargeable batteries become worse after multiple charges, unlike when the battery was first made, then the Anode is regaining the ions it lost, these ions are getting deposited on the anode somewhat randomly, which over time as this random deposition builds up it reduces the efficiency of the battery.


It’s about the particular chemistry of the batteries. We actually regularly recharge “non-rechargable” batteries on a very gentle trickle charge – especially AAs. They don’t hold up as well as those sold as rechargeables. But, we get a few more uses out of them. Batteries sold as rechargeables are designed with chemistry to allow the reaction of chemical –> electrical energy to be reversed numerous times without losing capacity. Non-rechargables aren’t optimized for this. But, it still works a few times.


With the topic of recharge-ability thoroughly covered you might also be wondering why if rechargeable batteries exist we still use single-use ones. The answer for that is two things: First, as batteries discharge they produce less voltage until they’re dead. Rechargeable batteries generally start dropping faster even if they take the same amount of time to “die”. Every device has a voltage level where it stops functioning. Thus some types of devices work for less time on rechargeables compared to single-use. This can be a problem if for example you’re going camping and need your flashlights to last all week. Second, some devices draw more current from their batteries than others and this can damage rechargeable batteries depending on chemistry, reducing the total lifespan of the battery even across multiple charges. These devices often specifically say not to use rechargeables in them.


The shortest answer to your question is that rechargeable chemistries have much lower energy densities than non-rechargeable ones. Almost without fail, across the board. They also tend to be more reliable (I’ve had tons of failed rechargeable AA cells) and can be stored for much longer before being used. A non-rechargeable lithium battery has a far higher energy content than a rechargeable one of the same size. Ditto for common batteries like coin cells, AA, AAA, etc. Batteries are cheap and most people would rather just replace the batteries in their TV remote every 3 years instead of recharging them every 6 months. As for the specific differences in terms of chemistry and whatnot I think the other comments cover it pretty well.