After a jump start, is driving around for an hour actually equivalent to putting the battery on a charger?

They are genuinely different, and the difference is that an alternator is a maintainer, not a charger.

An alternator is designed to replace what starting the car used — a small amount — and then run everything electrical while holding the battery topped up. It puts out a roughly fixed voltage and it is happy doing that all day. It was never designed to refill a deeply discharged battery, and it does that job badly.

A proper charger is different in two ways that matter. It steps through stages: a bulk phase at higher current, then a lower absorption phase held for a long time, then a float. And it takes hours in the later stages deliberately. Those slow final stages are where the last 20% of capacity actually goes back in — the part that decides whether the battery starts the car on a cold morning in February.

So your friend is right about the mechanism and you are right that it worked. Driving got you most of the way. It did not get you all of it, and the last part is the part that ages the battery if it is never completed.

On question 2, the kind of driving matters more than the hour does.

At idle or crawling in traffic, the alternator is spinning slowly and the car is also running the biggest loads it has — headlights, heater blower, heated rear screen, wipers. In winter, in traffic, at night, it is entirely possible for the car to be consuming everything the alternator makes and taking the remainder from the battery. An hour in that situation can leave you slightly worse off than you started.

An hour at steady speed with the lights off and the heater low is a completely different hour. Same clock, several times the charge.

So the advice should be "drive for an hour on an open road", and the version most people follow is "sit in traffic for an hour", which is why it sometimes appears not to work at all.

Answering 3 directly: yes, and the reason is what a flat battery is, not what it is missing.

A lead-acid battery left deeply discharged starts forming hard sulphate crystals on the plates. Recharging promptly reverses most of that; leaving it partially charged lets it set. A battery that is habitually run to 80% and topped back to 90% by driving is quietly losing capacity, and you find out on the first genuinely cold morning.

So an overnight charge after a flat battery is not belt-and-braces, it is the part that undoes the damage. It costs you nothing but the socket.

And worth saying: something flattened it. If you left a light on, fine. If nothing was left on, then either the battery is at the end of its life or something is draining it, and a charger will not fix either of those — it just delays the next time you need a jump.

One safety note since jump starting came up: modern cars would rather you used the designated jump points than the battery terminals directly, and many have a marked positive post under a plastic cover and a separate earth stud specifically for this.

It is not fussiness. Connecting straight to the terminals on a car with a battery monitoring sensor on the negative lead bypasses the sensor, and the car then has no idea what state the battery is in — some will undercharge it for weeks afterwards.

Worth thirty seconds in the handbook before the next time, not after.