That wouldn't be a very good assumption. People make assumptions based on other electric applications. LED lights are really bright and use no power. Lots of electric power tools and cars make it look like airplanes are the same and the whole industry will fall to this amazing new technology. It is creating a flood of people investing in pipe dreams.I assume we can fly 6 hrs with an electric plane that costs 20 k in two years.
Truth is airplanes need to make power, continuous power, Watts are Watts, HP is HP. Batteries are only as good as the chemistry. When you push the chemistry they get dangerous. When they get dangerous they need to be contained. When they have to be contained and managed the energy density starts to plummet. When that gets solved, tested, and gets in volume production then it still at the moment needs heavy containment.
So how is the chemistry going to change? Lithium is the current workhorse. What other technologies are leading the charge. You have exactly one periodic table to work with. Volatility is what it is.
Have you ever been around a Lithium based battery that started to overheat and run away. I have. You don't want that inside your fuselage. Boeing found out the hard way and they are really smart people. And they weren't using it for thrust.
$20k will not buy you the batteries, or the motor right now, nor in 10 years. You will not produce an airframe, especially certified and sell it for less than, I'll guess $250k, for the next 10 years.
So you can stop assuming.