C-Rate
C-rate is a charge or discharge current normalized to a battery's rated ampere-hour capacity.
What the number means
At 1C, the current in amperes is numerically equal to the rated capacity in ampere-hours. A 100 Ah battery is therefore charged or discharged at 100 A at 1C, 50 A at 0.5C, and 200 A at 2C. This current-based definition is the canonical basis.
Power divided by energy capacity, such as 150 kW divided by 75 kWh, can provide an approximate C-rate. The comparison is only meaningful when the power and energy figures describe the same battery level and capacity basis. Pack voltage changes with state of charge, so a fixed power does not imply a fixed current or exact C-rate throughout a charging session.
The inverse of C-rate gives an idealized time. A constant 1C rate would correspond to one hour, but an EV does not normally hold its peak rate from empty to full. Voltage limits, thermal control, charge taper, usable operating windows, and losses make actual charging time different.
For charging limits and curves, see Battery Charging.