An EV for example: if the car has 10% charge left, does the battery have less power or amps or whatever than it does when it’s at 90%? Or an iPhone at 20% vs 80%…same question. Or, from the battery’s perspective, even to 1% left, it’s either on or off, regardless of charge remaining?
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No, they don’t! Different kinds of battery chemistry have a different “discharge voltage curve” where the voltage delivered will gradually drop off as the battery’s charge decreases.
You can look up graphs to show general trends of different battery types but something like lead-acid will be a steady dropping curve while lithium-ion tends to stay high then take a sharp drop off around 80% discharged.
All that being said there are ways to mitigate this (circuitry to normalize voltage) and there is no guarantee that something like a smart device is telling you the raw discharge potential of the battery. A smart phone is unlikely to let you discharge a lithium-ion battery all the way to zero, so it would likely show you 1% charge left around that 20% remaining before the sharp drop in voltage where it likely can’t effectively function. It would also likely have the smarts to prevent damaging the battery with excessively deep discharge or overcharging.
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