[ranman]

Just to clarify -- it does not maintain that power. It will quickly ramp up to that on empty-ish batteries (320 amps at 320 volts is max that I know of) and maintain that until the battery is ~50% full. It will then ramp down and charge more slowly. While I can make lots of guesses as to why they charge in this way I don't know for sure on any of them.

[flyinglizard]

This is how Lithium batteries are charged - CC/CV. You first have constant current stage, then as the battery fills up you shift into constant voltage stage where the current is gradually reduced until the battery is full.

However CC/CV change doesn't normally happen at 50%, but further down the charging cycle. It may be that Tesla throttles the current ahead of time due to thermal constraints of the charging system.