No more than a pot on induction. Or for that matter, no more than with propane, or friction, or pressure, or with a mini-sun. Takes the same amount of energy regardless hah.

Speaking of which, this is a pretty cool tool: https://www.omnicalculator.com/physics/water-heating

So for 1 liter in my case, a 2K watt inverter woth 80% efficiency across the system would take under 4 minutes to boil.