chemical reactions are atoms exchanging electrons, all a battery does is force the atoms to exchange electrons through a wire

it's cheaper and more efficient to use a relay.

They have effectively zero contact resistance, but can switch the current only so fast and only do that so many times before wearing out and are fairly noisy, but even if they fail, they are readily available and easily replaced. This means compromises have to be made on the switching speed

if you wanted to have more granular control you would need power transistors/triacs to be able to switcher the current fast enough to modulate power, these would be more expensive, and less efficient, wasting power and requiring heat sinks for the components and extra circuitry to drive them correctly, increasing costs with no benefit as the food doesn't really care about how power is regulated

induction stoves need high frequency switching to work so they must use electronics, so they always have actual power control rather than "bang-bang" control

it depends what that path does, it can add 100 MB of new content, or it can replace a 100 MB file to fix bugs or improve things, or anywhere in between, it could replace a 50 MB file and add 50 MB of new content

because the first conputers used vacuum tubes, which ate a few centimeters in size, but we've invented transistors, which a much better alternative, that can do the same job but is only nanometers in size, and this means we can fit billions in less than a space smaller than single vacuum tube