The battery charging time calculator below works out how long a Li-ion, LiFePO4, NiMH or sealed lead-acid battery takes to charge from its capacity, the charge current and where it starts. Lithium and lead-acid results split out the constant-current phase and the slower constant-voltage taper.
A 100 Ah battery is 100000 mAh.
Optional: where the charger stops. Blank uses 0.05C, or 0.03C for lead-acid.
Optional: charge level where the voltage limit is reached, from your cell’s curve. Blank estimates it.
Optional: Ah put in per Ah stored. Blank uses 1.0 for lithium, 1.2 for NiMH, 1.11 for lead-acid.
Estimated charge time
2 h 28 min
Charge Li-ion only inside the cell’s rated temperature range, commonly 0 to 45 °C (the Panasonic NCR18650B sheet lists 10 to 45 °C). Never trickle charge a full cell.
Estimated CC to CV change at 85 % charge and a single-exponential taper to 150 mA. A real taper is not a pure exponential, so treat the time as an estimate.
A cell below its pre-charge threshold starts at a reduced current, which adds some minutes that are not included here. Three of the four standard versions of Microchip’s MCP73831 use 10 % of the programmed current for this.
Li-ion / LiPo charge time by charge rate
| Charge rate | Current | CC phase | Total |
|---|---|---|---|
| 0.1C | 300 mA | 8 h 30 min | 10 h 35 min |
| 0.2C | 600 mA | 4 h 15 min | 5 h 38 min |
| 0.3C | 900 mA | 2 h 50 min | 3 h 55 min |
| 0.5C | 1.5 A | 1 h 42 min | 2 h 28 min |
| 0.7C | 2.1 A | 1 h 11 min | 1 h 53 min |
| 1C | 3 A | 48 min | 1 h 26 min |
Charge time ≈ capacity × fraction to charge × charge factor ÷ current, plus a constant-voltage taper for lithium and lead-acid. A 3000 mAh Li-ion cell at 1.5 A (0.5C) takes about 2 h 28 min from empty: 1 h 42 min at constant current to about 85 %, then 46 min of taper.
The constant-current part is simple charge accounting. NiMH charging is entirely this part.
After that, Li-ion, LiFePO4 and lead-acid are held at their voltage limit and the current tapers. The calculator models the taper as a single exponential from I down to the termination current that delivers the remaining charge:
The transition point x is empirical. By default it is 85 % for Li-ion up to 0.5C, falling to 70 % at 2C; 95 % for LiFePO4 up to 1C, falling to 80 % at 4C; and for lead-acid 72 % at 0.1C, falling to 58.5 % at 0.25C. The straight lines between those points are an estimate, so enter x from your own cell’s curve if you have it. The result shows a range for x 10 points either way.
At 1.5 A the voltage limit arrives near 85 %: t_cc = 3 Ah × 0.85 ÷ 1.5 A = 1 h 42 min. With a 150 mA cut-off, τ = 3 Ah × 0.15 ÷ 1.35 A = 0.333 h, and t_cv = τ × ln(10) = 46 min. The total is 2 h 28 min.
NiMH has no taper, and timed charges use 120 % input. t = 2.5 Ah × 1.2 ÷ 0.5 A = 6 h, at 0.2C. That is below C/3, where there is no reliable end-of-charge signal and a timer has to stop the charge.
1.75 A is the 0.25 CA limit Yuasa gives for its NP batteries. About 58.5 % goes in at constant current in 2 h 36 min (with a 1.11 charge factor), and the taper to 210 mA adds 4 h 27 min, for 7 h 3 min. Float charging takes over after that.
What the charge time calculator gives with default settings for each chemistry, 0 % to 100 %. C-rates outside a chemistry’s usual range are shown as a dash.
| Charge rate | Li-ion / LiPo | LiFePO4 | NiMH | Sealed lead-acid |
|---|---|---|---|---|
| 0.05C | — | — | — | 23 h 57 min |
| 0.1C | 10 h 35 min | — | 12 h | 13 h 21 min |
| 0.2C | 5 h 38 min | 5 h 13 min | 6 h | 8 h 5 min |
| 0.25C | 4 h 36 min | 4 h 12 min | 4 h 48 min | 7 h 3 min |
| 0.5C | 2 h 28 min | 2 h 9 min | 2 h 24 min | — |
| 1C | 1 h 26 min | 1 h 6 min | 1 h 12 min | — |
| 2C | — | 38 min | — | — |
Published charge times are limits or read off charts by eye, so treat this as a sanity check. The model lands on both sides of them, up to about 20 % away. The Samsung figures come from the public retailer listings cited on the battery pack calculator.
| Battery and charge | Model | Published |
|---|---|---|
| Panasonic NCR18650B, 975 mA, 65 mA cut-off | 4 h 25 min | About 4.1 h on the datasheet chart |
| Samsung 30Q, 1.5 A, 150 mA cut-off | 2 h 28 min | 180 min |
| Samsung 30Q, 4 A, 100 mA cut-off | 1 h 14 min | 70 min |
| A123 26650, 10 A to 80 % | 12 min | 12 min |
| A123 26650, 2.5 A CCCV | 1 h 6 min | 60 min |
| Yuasa NP, 0.25C at 2.4 V/cell, to 0.03 CA | 7 h 3 min | About 8 h on Figure 12 |
| Yuasa NP, 0.1C at 2.4 V/cell, to 0.03 CA | 13 h 21 min | About 12 h on Figure 9 |
For a constant-current charge, the battery charge time formula is: time in hours = capacity in Ah × fraction to charge × charge factor ÷ charge current in A. Lithium and lead-acid batteries then spend extra time in a constant-voltage taper, which this calculator adds.
About 2 h 28 min from empty at 1.5 A (0.5C) with a 150 mA cut-off: 1 h 42 min of constant current, then 46 min of taper. Getting to 80 % takes only 1 h 36 min. A public retailer listing for the Samsung 30Q gives 180 minutes for this charge.
Once a lithium cell reaches its voltage limit, the charger holds that voltage and the current falls as the cell fills. Battery University notes that raising the charge current does not hasten full charge by much: the constant-current stage is shorter, but the saturation stage takes longer.
Follow the datasheet. Typical energy cells are charged at 0.5C to 1C: the Panasonic NCR18650B has a 0.5C standard charge, and a retailer listing gives the Samsung 50E a 1C maximum. Some power cells allow more (the Samsung 30Q is listed with a 4 A, about 1.3C, rapid charge).
An A123 26650 cell (2.5 Ah) takes about 1 h 6 min from empty at 2.5 A (1C) with the default model, and A123 publishes 60 minutes for that charge. At 10 A it reaches 80 % in about 12 min.
Divide capacity by current and multiply by about 1.2 for losses. A 2500 mAh cell at 500 mA takes 6 h. Below about C/3, chargers rely on a timer because there is no clear end-of-charge signal.
About 7 h 3 min from empty at the 1.75 A (0.25C) that Yuasa recommends. Yuasa’s published curve at that rate returns 100 % of the discharged charge in about 6 hours, and the current falls to 0.03 CA after about 8 hours.
Yes. Whatever the device draws comes out of the charger’s current, and it can stop the taper from reaching the termination level. Battery University advises turning the device off or disconnecting the load during charge.
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