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Category Electronics

Presets:

Capacity Unit

Battery Capacity Enter value from battery label

Nominal Voltage V Typical: 3.7V (phone), 11.4V (laptop), 400V (EV)

Charger Unit

Charger Output

Current Charge Level %

Target Charge Level %

Charging Efficiency: 85%

50% (Wireless/Old)85% (Typical)99% (Ideal)

Apply CC/CV taper correction (recommended for Li-ion)

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About

Estimating battery charge time requires more than dividing capacity by current. Real lithium-ion cells follow a two-phase Constant Current / Constant Voltage (CC/CV) protocol: the charger delivers full current until the cell reaches roughly 80% state-of-charge, then tapers current logarithmically to avoid lithium plating. Ignoring this profile underestimates total charge time by 25 - 40%. Thermal losses, cable resistance, and voltage conversion further reduce effective charging efficiency η to 0.80 - 0.90 for typical USB-PD adapters. This calculator models both the CC linear phase and the CV taper phase, applies a user-adjustable efficiency factor, and outputs a realistic time window rather than an idealized minimum.

Misestimating charge duration has practical consequences: leaving for a trip with a half-charged EV, over-scheduling equipment turnaround in field operations, or undersizing a solar charge controller. The tool accepts inputs in mAh or Wh, handles charger specs in A or W, and includes presets for common devices. Note: the CC/CV taper model is a first-order approximation. Real charge curves vary by cell chemistry (LFP cells have a flatter voltage plateau) and battery management system firmware.

Formulas

The fundamental charge time equation divides the energy deficit by the effective charger delivery rate:

T = C × (SoC_target − SoC_current)I × η × 100

Where T = charge time in hours, C = battery capacity (mAh or Wh), SoC_target = target state of charge (%), SoC_current = current state of charge (%), I = charger output current (A) or power (W), and η = charging efficiency (0 - 1).

When charger output is specified in watts, the effective current is derived from the nominal battery voltage:

I_eff = P_chargerV_nominal

Where P_charger = charger output power (W) and V_nominal = nominal battery voltage (V).

The CC/CV taper correction splits the charge into two phases. For a target above 80%, the CV phase adds additional time:

T_total = T_CC + T_CV

T_CV ≈ T_rate × 1.5 × (SoC_target − 80)100

Where T_rate is the time-per-percent at full CC rate and the 1.5 multiplier approximates the logarithmic taper in the constant-voltage phase. This model assumes a standard Li-ion CC/CV profile. LFP chemistry cells maintain CC longer and have a sharper CV cutoff.

Reference Data

Device Type	Typical Capacity	Common Charger	Approx. 0→100% Time	Efficiency	Chemistry
Smartphone (Standard)	4000 mAh	10 W	2.0 - 2.5 hr	85%	Li-ion / Li-poly
Smartphone (Fast Charge)	5000 mAh	65 W	0.5 - 0.8 hr	82%	Li-poly
Tablet	8000 mAh	20 W	2.5 - 3.5 hr	85%	Li-poly
Laptop (Ultrabook)	56 Wh	65 W	1.2 - 1.8 hr	88%	Li-poly
Laptop (Workstation)	100 Wh	140 W	1.0 - 1.5 hr	87%	Li-ion
Power Bank (Small)	10000 mAh	18 W	2.5 - 3.5 hr	83%	Li-ion 18650
Power Bank (Large)	26800 mAh	30 W	4.0 - 5.5 hr	82%	Li-ion 21700
Drone Battery	5000 mAh / 77 Wh	100 W	0.8 - 1.2 hr	90%	LiPo
E-bike Battery	500 Wh	42 V / 2 A (84 W)	5.0 - 7.0 hr	88%	Li-ion
EV (Small, 40 kWh)	40 kWh	7.4 kW (L2)	5.5 - 7.0 hr	90%	NMC / LFP
EV (Mid, 75 kWh)	75 kWh	11 kW (L2)	7.0 - 9.0 hr	90%	NMC
EV (DC Fast, 75 kWh)	75 kWh	150 kW (DCFC)	0.5 - 0.7 hr (10→80%)	92%	NMC
EV (Large, 100 kWh)	100 kWh	250 kW (DCFC)	0.4 - 0.6 hr (10→80%)	93%	NMC
AA NiMH (Single Cell)	2500 mAh	500 mA	5.0 - 6.0 hr	80%	NiMH
12V Lead-Acid (Car)	60 Ah	10 A	6.0 - 8.0 hr	75%	Lead-Acid
Solar Power Station	2000 Wh	200 W (solar)	10 - 14 hr	78%	LFP

Frequently Asked Questions

Li-ion batteries use a CC/CV charging protocol. During the Constant Current (CC) phase (roughly 0-80%), the charger pushes maximum current and charge accumulates linearly. Above ~80%, the Battery Management System switches to Constant Voltage (CV) mode, tapering current logarithmically to prevent lithium plating and thermal runaway. This CV tail adds roughly 40-60% extra time relative to what a purely linear model would predict. The calculator applies a 1.5× time multiplier per percentage point above 80% SoC to approximate this behavior.

Efficiency η represents the ratio of energy stored in the battery to energy drawn from the wall. A typical USB-PD charger with GaN topology achieves 88-92% efficiency. Older 5V/1A adapters drop to 78-83% due to linear regulation losses. Wireless (Qi) charging ranges from 60-75% because of air-gap coupling losses. Every 5% drop in efficiency adds roughly 5-7% to total charge time. The calculator defaults to 85% but allows adjustment from 50% to 99% to model these scenarios.

Manufacturers label phone batteries in mAh (milliamp-hours) at nominal voltage (typically 3.7V for Li-ion). Laptop and EV batteries use Wh (watt-hours) because they operate at higher voltages. The relationship is: Wh = mAh × V ÷ 1000. A 5000 mAh phone battery at 3.7V nominal equals 18.5 Wh. When you select mAh mode, the calculator uses the nominal voltage you specify to convert internally. For accuracy, always match the capacity unit to what is printed on the battery label.

Yes, significantly. Li-ion cells charge optimally between 15-35°C. Below 10°C, internal resistance rises and the BMS reduces charge current to prevent lithium plating, potentially doubling charge time. Above 40°C, the BMS throttles current to avoid thermal degradation. This calculator does not model temperature directly but you can approximate cold-weather effects by reducing the efficiency slider to 65-70% and hot-weather effects by reducing it to 75-80%.

DC fast chargers (DCFC) use dynamic power curves that depend on battery temperature, SoC, and the vehicle's peak charge acceptance rate. A 150 kW charger may only deliver 150 kW between 10-50% SoC, then taper sharply. This calculator provides a first-order estimate assuming average power delivery. For EV planning, use the 10%→80% range (where DC charging is most efficient) rather than 0%→100%. The CC/CV model in this tool approximates the taper above 80% but real EV curves are more complex and vehicle-specific.

The battery's BMS limits incoming current regardless of charger capacity. A 100W charger connected to a phone that accepts maximum 25W will only deliver 25W. In this calculator, you should enter the actual charge rate the device accepts, not the charger's maximum rated output. Check your device specifications for maximum charging power. Entering the charger's rated wattage when it exceeds the device limit will produce an optimistically short (incorrect) time estimate.