How to Charge a 3.7V Li-ion Battery With TP4056

A TP4056 module lets you charge a single-cell 3.7V nominal lithium-ion battery, such as an 18650 cell, from a regulated 5V USB supply. Connect the battery to B+ and B-, then power the module through its USB input. The charger regulates the battery voltage to approximately 4.2V and controls the charging current.

This guide explains TP4056 wiring, the difference between modules with and without protection, charging-current selection using the RPROG resistor, LED indicators, and practical charging times for 2200mAh and 4000mAh batteries.

Important safety note: Never connect a 3.7V lithium-ion battery directly to a 5V phone charger. Use a compatible charging circuit, verify polarity, and never charge a swollen, damaged, leaking, or unusually hot cell.

Quick Answer: How to Charge a 3.7V Li-ion Battery

To charge a standard 3.7V nominal lithium-ion cell using a TP4056 module:

1. Connect the battery positive terminal to B+ and battery negative to B-.

2. Connect a regulated 5V USB supply to the module's USB port or its correctly labelled input terminals.

3. Check that the charging current configured on the module is suitable for the battery.

4. Observe the status LEDs, following the instructions for your specific module.

5. Allow charging to finish, and disconnect the battery or supply if the cell or module becomes unusually hot, swollen, or damaged.

A typical TP4056 charger is designed for a single lithium-ion or lithium-polymer cell with a full-charge voltage of 4.2V. It is not suitable for charging a multi-cell battery pack in series or a battery chemistry that requires a different charging voltage.

What Is the TP4056 Charging Module?

The TP4056 is a single-cell lithium-ion battery charger IC that uses a constant-current/constant-voltage charging method, commonly called CC/CV. Many small charging boards combine the TP4056 with a USB connector, status LEDs, and battery connection pads.

A typical module accepts regulated 5V input and charges a compatible cell to approximately 4.2V. The charging current is set by a resistor on the board, so not every TP4056 module necessarily charges at 1A.

Some modules also include a battery protection circuit, commonly built around a DW01A protection IC and a dual MOSFET such as the 8205A. This protection circuit is separate from the TP4056 charging function.

TP4056 module with protection vs without protection

Check the actual board before wiring. Terminal labels and protection features can vary, and a module's protection circuit does not replace safe charging practices or a suitable battery.

TP4056 Pinout and Wiring

The terminal labels determine where the USB input, battery, and load should connect. Do not assume every TP4056 board uses the same layout.

If your module has a USB connector, it may be more convenient to use that for the 5V input instead of the IN+ and IN- pads. Follow the board's markings.

Wiring an 18650 battery to a TP4056

For a protected TP4056 module:

1. Connect the positive terminal of the 18650 cell to B+.

2. Connect the negative terminal of the cell to B-.

3. Connect the load to OUT+ and OUT- if the module documentation specifies these as the protected output terminals.

4. Connect a regulated 5V USB supply to the module's USB input.

5. Check the polarity and all connections before applying power.

On a protected board, connect the load to the designated OUT terminals rather than bypassing the protection circuit through B+ and B-. On a board without protection, do not assume the battery terminals provide protected output. Use an appropriate protection arrangement for the battery and load.

Never connect a 5V source directly across the battery terminals. The USB supply must feed the TP4056 input, which controls the charging process.

Charging a 3.7V Battery With a TP4056: Wiring Diagram in Words

The connection path is straightforward:

• USB 5V supply to TP4056 input: Provides power to the charger.

• TP4056 B+ to battery positive: Connects the positive battery terminal.

• TP4056 B- to battery negative: Connects the negative battery terminal.

• TP4056 OUT+ and OUT- to the load, when provided: Supplies the connected project through the board's protection circuit.

The TP4056 is designed for one cell with a nominal voltage of 3.7V and a full-charge voltage of approximately 4.2V. It is not a boost converter, so it does not turn the battery's output into a regulated 5V supply. If your project needs a steady 5V output, use a suitable boost converter or power-management circuit.

Charging Current: Choosing the Right RPROG Resistor

The TP4056 uses a programming resistor, usually marked RPROG or shown as a resistor near the charger IC, to set its charging current. Many common modules are configured for approximately 1A, but the exact value depends on the board's resistor and design.

Typical current settings are shown below as approximate examples. Verify the resistor value and current-setting formula for the specific TP4056 version used on your board.

A higher programming-resistor value generally sets a lower charging current. A lower value generally sets a higher current, within the IC and module's limits.

How to choose the current for your battery

Check the battery manufacturer's datasheet for its recommended charge current. Do not select the current based only on the battery's physical size or the TP4056 board's maximum rating.

For example:

• A 2200mAh cell charged at 1A is charged at roughly 0.45C.

• A 4000mAh cell charged at 1A is charged at roughly 0.25C.

Here, C-rate expresses the charging current relative to the battery's capacity. Whether either rate is suitable depends on the specific cell's datasheet and condition.

The TP4056 is a linear charger and can generate heat while charging. If the board becomes hot, the IC may reduce the charging current through thermal regulation. Do not assume a module will sustain 1A continuously under every condition.

Only change the programming resistor if you understand the circuit and can safely modify the board. Disconnect USB power and the battery before soldering, and avoid accidental short circuits.

How Long Does It Take to Charge a 2200mAh or 4000mAh 18650 Battery?

Charging time depends on the battery's capacity, the selected charging current, its initial voltage, temperature, and the constant-voltage phase near full charge.

A simple estimate is:

Ideal charging time (hours) = Battery capacity (mAh) ÷ Charging current (mA)

For example, a 2200mAh battery charged at 1000mA gives an ideal estimate of 2.2 hours. Actual charging takes longer because the TP4056 reduces current as the battery approaches 4.2V.

These are approximate estimates, not guaranteed charging times. A deeply discharged, aged, cold, or warm battery may charge differently. The charger may also reduce current because of its own temperature.

Do not force a higher current to shorten charging time unless the battery's specifications and the charging board support it.

TP4056 LED Indicators: Red, Blue and Green

Many TP4056 modules use two LEDs to indicate charging status. The exact colours and behaviour vary by board.

Common behaviour is:

• Red LED on: Charging is in progress.

• Blue or green LED on: Charging has completed.

• Both LEDs off: The board may have no input power, no connected battery, or a different status depending on its design.

Use the board's documentation rather than relying on LED colour alone. A light indicating charge completion does not prove that the battery is healthy, and an LED that stays off does not always mean the battery is fully charged.

If the LEDs behave unexpectedly, disconnect the power if you notice heat, swelling, damage, or an unusual smell. Otherwise, check the USB input, battery polarity, terminal connections, and the module's instructions.

Charging Multiple 18650 Batteries With a TP4056

A standard TP4056 is designed to charge one lithium-ion cell at a time. It is not designed to charge two cells connected in series.

Connecting cells in series increases the pack voltage. A two-cell series pack has a nominal voltage of around 7.4V and reaches approximately 8.4V when fully charged, so it cannot be charged using a standard single-cell TP4056 module.

Charging multiple cells in parallel also requires care. The cells should be suitable for parallel operation, matched in chemistry and condition, and brought to compatible voltages before connection. The charging circuit and protection arrangement must be designed for the resulting pack.

For multi-cell batteries, use a charger and battery-management system specifically designed for the pack configuration. Do not improvise a multi-cell charging circuit by joining several TP4056 boards to a pack.

Can You Power a Project While Charging?

Some TP4056 boards allow a load to be connected to their output terminals, but a basic TP4056 charger does not provide a proper power-path management function. A connected load can interfere with charge termination or cause the battery to remain in an unexpected charging state.

For a project that must operate while the battery charges, use a charger or power-management circuit with a suitable power-path feature. Check the module documentation before connecting a load during charging.

Also remember that a single 3.7V nominal cell does not provide a regulated 5V output. If your Arduino, ESP32, or other device needs a stable supply voltage, use a suitable regulator or boost converter and ensure that the full battery-voltage range is supported.

Common TP4056 Charging Problems and Fixes

The battery does not charge

Check that the USB supply provides the correct input voltage, the battery is connected with the correct polarity, and the board's input and battery terminals are wired correctly. If the battery is damaged or has been discharged below its safe operating range, do not attempt to recover it without appropriate equipment and guidance.

The TP4056 module gets too hot

The TP4056 dissipates heat while charging, particularly when the input voltage is much higher than the battery voltage or the charge current is high. Use a suitable current setting, allow adequate ventilation, and follow the board's thermal limits. Stop using the module if it becomes excessively hot or shows signs of damage.

The charging LED never changes

The battery may not have reached the termination conditions, the selected charging current may be too low, or the connected load may interfere with charging. Verify the battery and module specifications, and disconnect any load if the board's instructions recommend charging without one.

The battery gets hot, swells, or smells unusual

Disconnect the input power if it is safe to do so, stop using the battery, and keep people away from the damaged cell. Do not puncture, compress, or continue charging it. Follow local guidance for safe lithium-ion battery handling and disposal.

Recommended Products for a 3.7V Battery Charging Project

For a single-cell battery project, select a compatible battery, charging module, and holder. Confirm the module's protection features and the battery's charging specifications before use.

Check the current product listings for the exact specifications, battery chemistry, protection features, connector type, and availability. Do not assume every 18650 cell or TP4056 board has the same capacity, protection circuit, or charging-current setting.

Conclusion

The TP4056 is a practical way to charge a single-cell 3.7V nominal lithium-ion battery from a regulated 5V USB supply. Connect the battery to B+ and B-, use the correct input terminals, and choose a charging current that the battery can safely accept.

For 18650 cells, remember that capacity affects charging time, the RPROG resistor controls the charging current, and the protection features depend on the exact module. Use a compatible protected charging arrangement, avoid charging damaged cells, and never connect a 5V supply directly to the battery.