Battery Charge Time (mAh)

Charging time from mAh: theory vs reality

The base formula is charge_time_h = capacity_mAh / charger_current_mA. In practice you'll want to multiply that by 1.3-1.5, because chargers follow the CC-CV curve. They push constant current up to around 80%, then taper off into constant voltage, which is what drags out the final 20%. The C-rate tells you how fast that happens: 1C fills the whole battery in an hour, 2C in 30 minutes. Take a 5,000 mAh phone on a 30 W fast charger (~5.5 A at 5 V). It reaches 80% in about 50 min and 100% in roughly 75. A Tesla Supercharger V3 (250 kW) moves a Model 3 from 10 to 80% in 20-25 min, while domestic Level 1 charging (2.3 kW at 220 V/10 A) needs around 25 h for the same thing. As for standards, USB-PD goes up to 240 W, Qi wireless sits at 5-15 W, and Apple MagSafe at 15 W. Fast charging only buys you speed early on; that last 20% stays slow on purpose, to protect the cells.

Applications

Planning EV trips, sizing a fast charger (USB-PD 240 W), working out wireless Qi and MagSafe times, estimating power-bank top-ups, and sizing a solar charging setup.

FAQ

Why does the last 20% take so long? Near full charge the CC-CV curve cuts the current to keep heat and degradation down. The 80-100% leg can easily take as long as 0-80% did.

Does a more powerful charger always charge faster? Only up to whatever the device will accept. Plug a 100 W charger into a phone capped at 25 W and it just delivers 25 W.

Does fast charging damage the battery? It speeds up wear a little, since it runs hotter, but modern chips keep the temperature in check. For typical use the real-world impact is small.