Battery Charge Time

Formula

Description

Charge time estimates how long it takes to fully charge a battery at a given constant current. This is a simplified model because real charging profiles are not constant current throughout. Lithium-ion batteries use CC-CV (constant current then constant voltage) charging, where the current tapers during the CV phase, adding 30-60 minutes to reach full charge. The practical charge time is typically 1.2-1.5 times this theoretical value. Fast charging at higher currents reduces time but generates more heat and may reduce cycle life.

Variables

• t — Approximate charge time (h)
• Capacity — Battery capacity (mAh)
• Icharge — Charging current (mA)

Practical Notes

Standard lithium-ion charging is at 0.5C to 1C (where C is the capacity in Ah). A 3000mAh cell at 1C charges at 3A. Fast charging protocols (Qualcomm QC, USB-PD) use higher currents or voltages. NiMH batteries can be charged at up to 1C with proper termination. Lead-acid batteries charge best at C/10 to C/5 rate.