Battery Charge Time Calculator

Battery recharge time: the CC-CV curve

The base formula is t = capacity / (current · efficiency). Real chargers don’t behave that cleanly, though. They follow a CC-CV profile, holding constant current up to roughly 80% state of charge, then switching to constant voltage with a current that tapers off through the last 20%. So bump the theoretical figure up by 1.3-1.5x. Take a 30 W USB-PD fast charger: it gets a phone to 80% in about 50 minutes, then spends another 30-40 minutes crawling to 100%. A Tesla Supercharger V3 (250 kW) takes a Model 3 from 10% to 80% in roughly 20 minutes, and that 80-100% stretch by itself eats another 20-30. How much you actually get depends on cable losses, thermal throttling and the ambient temperature.

Applications

Working out when a phone will be ready off a fast charger, planning EV stops on a trip (Tesla, BYD, VW ID), timing the charging windows on an e-bike or electric scooter, rotating drone batteries on a photo shoot, or just guessing how long a power bank needs to top up.

FAQ

Why charge to only 80%? That final 20% is where charging is slowest and hardest on the cells. On road trips, plenty of EV owners pull the plug at 80% and save themselves 20-30 minutes per stop.

Does the cable matter? It does. Without the e-marker chip, a USB-C cable tops out at 3 A. Anything past 100 W needs a cable rated for 5 A.

Why does charging slow down in summer? When the pack gets hot, the battery management system pulls back the current to protect how long the cells last. Parking in the shade or running active cooling helps.