400V vs 800V architecture
The battery system voltage an EV is built around. At the same power, an 800V system needs about half the current of a 400V one, which can help fast charging.
EVs are built around a nominal battery voltage. The US Department of Energy says high-voltage systems in electric and hybrid vehicles typically range from 400 to 1,000 volts, and its 2017 fast-charging assessment describes 400 V as the industry standard at the time, with 800 V as the higher-voltage alternative.
The appeal of doubling voltage is physics. Power is voltage times current, so at the same charging power an 800 V pack draws about half the current of a 400 V one. The assessment says higher currents generate more heat and need more robust internal parts, adding weight and cost, and that a higher charging voltage reduces the cable size between charger and vehicle. Some fast-charging times may therefore benefit from 800 V, depending on the car.
The catch is compatibility: the same report calls interoperability between vehicles and chargers with different voltage and current ratings a main challenge, so check the charger's ratings too. In day-to-day AC charging at home, the pack voltage is not the deciding spec. Treat 800 V as most relevant to frequent road-trippers.