This small breakout board is a highly flexible charger for 2-4S LiIon battery packs.
It can be powered via USB-C port or via a fixed input voltage in the range of 5-20V. The board supports USB-PD, and when you power it via its USB-C input, it automatically negotiates the most efficient input voltage.
Boards come preconfigured for 2S, 3S, or 4S LiIon battery packs. Make sure you order the version you need. By manually replacing two (tiny) resistors, you can re-configure the board for 1S and 5S, and you can change the chemistry from LiIon/LiPo to LiFePo4.
Overview
This board is a Chinese product with an unknown (and undocumented) power management chip. Considering its price (around €2.00), it is an excellent value and may be your one-stop solution to charge 2-5S LiIon/LiPo/LiFePo4 battery packs conveniently via USB.
Unfortunately, not all the options supported by the power management chip are available for order. 1S and 5S as well as the option to use LiFePo4 require manual replacement of two resistors on the board.
This is a charger only: the USB-C port is unidirectional and can be used for charging only. This board is not a discharger. If you want to built a power bank and supply USB power from your battery pack, look at charger-discharger boards.
| Item | Description |
|---|---|
| Voltage Input | 5-20V, USB PD |
| Voltage Output | 2S, 3S, or 4S (preconfigured) |
| Charger | LiIon/LiPo LiFePo4 requires changes on the board |
| LEDs | 3 LEDs, indicating charging, quick charge, and fully charged |
| Protections | Over-Temperature, Short-Circuit This board is no BMS, you will still need a separate BMS board for your battery pack |
Heat Generation
This is a very efficient synchronous converter board that can reach 98% efficiency. Excess heat generation is low under these circumstances.
However, the charger can get quite hot (>70C) if you force it to boost a large voltage gap. So if you i.e. supply just 5V via a basic USB power supply, and charge a 4S battery pack, then make sure to add additional heat sinks.
The best way to keep the module temperature low is to use a modern USB PD power supply in which case the charger negotiates a higher voltage and can work efficiently.
Connections
Connect the battery to B+ and B-. Make sure you are using a separate BMS board with balancing capabilities.
Input power can either be supplied via USB-C, or via the dedicated VIN+ and VIN- pads (5-15V).
Additional Solder Pads
On the back side, B, G, and Rcan be used to connect external LEDs.
On the front side, located between B+ and B-, additional unmarked solder pads can be used to add a thermistor.
Connecting a temperature probe is not enough, though. Using a temperature sensor requires changing the NTC voltage divider resistor on the board (unfortunately no documentation exists).
Indicator LEDs
The board comes with three LEDs in different colors:
| LED | Description |
|---|---|
| green | on: fast charge or no battery connected 4Hz flash: battery short circuit |
| red | on: charging |
| blue | blinking: negotiating fast charge on: fully charged |
The LEDs are labeled on the PCB backside (however in Chinese):
On the backside of the board, three through-hole solder pads labeled R, G, and B exist that can be used to connect external LEDs (remove the onboard LEDs).
Battery Chemistry and Strings
This breakout board is sold preconfigured for LiIon chemistry and 2S, 3S, or 4S configuration. These boards cover only a fraction of the use cases that the power management IC can handle.
Manually Re-Configuration
Regardless of battery chemistry or string count, from the charger perspective, the only thing that matters is the battery cut-off voltage. That’s the voltage that indicates a full charge.
Technically, this charger supports cut-off voltages from 3.6-21.0V, so this charger can handle 1-5S both for LiIon/LiPo and LiFePo4. At least this is what sellers claim.
According to the seller, the cut-off voltage is set using two resistors (R1 and R2), and can be fine-tuned using a third resistor (R2').
The general formula to calculate the cut-off voltage is:
Vcutoff = 1.8V * (1 + (R1/R2))
These are the resulting values for the most common configurations:
| Charging Cut-Off Voltage (V) | Chemistry | Strings | R1 (top) | R2 (bot) | R2’ |
|---|---|---|---|---|---|
| 3.60 | LiFePO4 | 1S | 100K | 100K | - |
| 3.65 | LiFePO4 | 1S | 25K | 30K | 180K (trim) |
| 3.70 | LiFePO4 | 1S | 56K | 59K | - |
| 4.10 | LiIon/LiPo | 1S | 39K | 7.50K | - |
| 4.20 | LiIon/LiPo | 1S | 27K | 20.0K | - |
| 4.35 | LiIon HV | 1S | 100K | 80.6K | - |
| 7.30 | LiFePO4 | 2S | 100K | 32.7K | - |
| 7.40 | LiFePO4 | 2S | 56K | 18.0K | - |
| 8.40 | LiIon/LiPo | 2S | 51K | 13.7K | - |
| 10.95 | LiFePO4 | 3S | 100K | 19.6K | - |
| 11.10 | LiFePO4 | 3S | 62K | 12.0K | - |
| 12.60 | LiIon/LiPo | 3S | 160K | 26.7K | - |
| 14.60 | LiFePO4 | 4S | 180K | 25.5K | - |
| 14.80 | LiFePO4 | 4S | 180K | 26.0K | - |
| 16.80 | LiIon/LiPo | 4S | 140K | 16.9K | - |
| 18.25 | LiFePO4 | 5S | 220K | 24.0K | - |
| 21.00 | LiIon/LiPo | 5S | 160K | 15.0K | - |
Caveat and Urban Legends
There is absolutely no documentation:
- There are no markings on the power management IC, so it is unclear which pin is the chip feedback pin (
FB) and what its specs really are. - There are no prints on the PCB, so it is unclear which resistors are
R1andR2.
When comparing images of different string-versions of this chip, there seem to be no resistor differences (except for the shunts), but possibly vendors reused the same image for different versions.
After investigating the traces with no luck, I decided to order a couple of different board versions myself to clarify if in fact there are configurable resistors, or whether possibly the different board versions use different chip versions with internal feedback circuitry. I’ll keep you updated as I go.
That said, all of this is for academic reasons and out of curiosity. I am quite happy with the preconfigured boards as-is. This works perfectly well for me out of the box.
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(content created Oct 12, 2025)