Why does an electric car charge fast to 80%, then crawl to full?

Plug a Tesla Model Y into a Supercharger near empty and it reaches 80% in about half an hour. The last 20% takes about as long again. Elon Musk explained it with a parking lot.

▶ Try it yourself in Charge Curve: fill the battery, watch the power fall, and plan a road trip with long or short stops.

What is the parking lot?

Charging pushes lithium ions into spaces in the battery’s anode. On Joe Rogan’s podcast in 2023, Musk compared them to cars looking for a space: when the lot is empty, they can “zip right in”, and as it fills, each one has to hunt around for a spot. He added that getting from 80 to 100 takes about as much time as getting from 0 to 80.

Why does the car turn the power down?

A fast charge starts at constant current, as much as the charger and pack allow. As the cells approach their maximum voltage, the car holds the voltage steady and lets the current fall. If it kept forcing ions in at full speed into a nearly full anode, some would deposit on the surface as lithium metal instead of slotting in. That plating costs capacity and can be a safety risk, and cold batteries plate more easily. Heat matters too.

How big is the slowdown?

EVKX’s measured curve for a Model Y Long Range shows 10 to 80% in about 32 minutes and 80 to 100% in about 31 more. Other cars differ: a Porsche Taycan reaches 80% in under 18 minutes, then needs about 29 to finish. Even CATL’s newest fast-charging cells, which it says go from 10 to 80% in 3 minutes 44 seconds, take nearly 3 more minutes for the next 18%.

Why do road trips use short stops?

Because the first part of the curve is the cheapest time you can spend. Tesla says its Superchargers can add up to 200 miles in 15 minutes and that charging above 80% is rarely necessary on a trip. Arriving low and leaving at 60 to 80% keeps every stop on the fast part of the curve, so several short stops usually beat one long one.

The tool uses an illustrative Model Y–like power curve fitted to those times, a 75 kWh pack and a fixed few minutes per stop to park and plug in. Real curves change with temperature, the charger and the car’s software. The film’s footage is a Supercharger plug-in by @zacharymorris, Musk on the Joe Rogan Experience (clip via @NarutoNolimits) and a measured curve posted by @TeslaClubIN; the parking lot is drawn, and the numbers come from the model.

Sources: Yahoo Finance, Musk on charging past 80% (2023); EVKX, Model Y Long Range charging curve; EVKX, Porsche Taycan charging curve; Fastned, Everything about fast charging; Tesla, Supercharger; CarNewsChina, CATL Shenxing (2026).