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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The battery by itself, no. It’s been covered by other comments but I think I can add 2 things. 1, a battery stores energy in chemistry. There are reactants that react together to make products. The speed of the reaction basically defines the voltage of the battery (well, I guess current more directly and voltage indirectly, but it works well enough for eli5). The higher the concentration of reactants and lower concentration of products the faster the reaction runs. As the reactants get transformed into products, the reaction slows down, decreasing the voltage that the battery can maintain.
But the battery is no longer an isolated component in modern circuits. There is always a governing circuit. It’s often some kind of voltage regulator that can take a small amount of the energy to hold the voltage more stable. There are even boost circuits that can raise the voltage at the cost of current. So there’s a high likelihood that the rest of your circuit sees the same voltage regardless of the charge on the battery… As long as you don’t run it beyond the designed parameters. However, the governing circuit should also monitor the charge of the battery and stop the circuit from using more than it’s designed to. It can help monitor charging current too so that the battery doesn’t explode (hopefully).
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