Why do rechargeable batteries (e.g., mobile phone batteries) need sometimes several hours to be fully charged? In other words, what are the physical constraints that don't allow me to charge my iPhone battery in 1 min, for instance?
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$\begingroup$ I'll leave a proper answer to someone who knows about batteries, but I will put a bet on the answer having to do with heat generation in the charging process. $\endgroup$– AsherCommented Jan 11, 2015 at 16:57
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I will give you an easy answer on the limit to charging rate, rather than the reasons for existing charging rates. If we assume a 2Ah battery capacity it means that it take (approximately) one hour at 2 amps to charge the battery. If, say, you wanted to charge it in a convenient 1 minute the battery would have to be fed with 120 Amps. That is far more than even domestic mains wiring is capable of taking, let alone the thing wire of existing wall wart chargers or the internal contacts in the phone electronics. The same kind of reasoning applies to electric car battery charging as well.
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1$\begingroup$ I highly doubt that mains wiring is unable to supply $\sim500\mathrm{W}$ of power (my electric teapot takes $2200\mathrm W$). You forget that mains gives you $110\mathrm V$ or $220\mathrm V$ but your charger supplies about $4\mathrm V$ to the battery, and $120\mathrm A$ is the current from charger to battery, not from mains to charger. $\endgroup$– RuslanCommented Jan 11, 2015 at 19:37
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$\begingroup$ @Ruslan the words used by Dirk Bruere emphasize that 120 A is a high current. He does not say that the domestic mains wiring will have to carry 120 A, he just makes the comparison that if you would use the same wiring of domestic mains wires for chargers, you still would not be able to carry that much current safely. I initially jumped to the same conclusion as you did, so Dirk Bruere could consider rephrasing that comparison. $\endgroup$ Commented Jan 11, 2015 at 20:02
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$\begingroup$ No, the mains would not have to carry 120A. If we take USA mains voltage it would have to supply around 2A before the transformer. The 120A would come after that. The problem is the low voltage used to charge the battery, which for a given power means much higher currents, which mean very thick wires. $\endgroup$– user56903Commented Jan 12, 2015 at 7:41