⚡ Lithium plating risk
As the anode fills up, lithium ions have fewer places to slot into. Push current too hard at a high state of charge and metallic lithium plates onto the anode instead — permanent capacity loss, and a dendrite/short risk. The BMS taper above roughly 60–80% is the insurance policy.
🌡 Heat
Fast charging dumps waste heat into the cells faster than the coolant loop can pull it out. A cold pack can't accept high current either (ion mobility collapses), which is why preconditioning on the way to a charger matters so much. Too hot or too cold, the BMS cuts power to protect the cells.
🔌 Voltage and current limits
Power = volts × amps, and a cabinet has a ceiling on each. Most 350 kW CCS cabinets top out near 500 A, so a 400 V-class car physically cannot exceed about 175–200 kW no matter what the sticker says; an 800 V car draws the same power at half the current and gets the full rating. Tesla went the other way — roughly 700 A but only 500 V — so a 400 V Tesla really does see 250 kW at a Supercharger, while an 800 V car plugged into one has to split its pack and settle for a fraction of its peak.
⏱ C-rate, not kilowatts
A charger's kW only means something relative to the pack it is filling. 250 kW into a 75 kWh Model 3 is 3.3C — ferocious. A 1.2 MW megawatt cabinet into a Tesla Semi's 850 kWh is 1.4C, which is why a megawatt still needs half an hour. Air taxis sit at the other extreme: tiny packs charged at 2–3C, several times a day, and replaced on flight hours rather than range loss.