Battery Stops Charging at 4.0 V (Expected 4.2 V Termination, 20% Termination Current)

[mhni]

Hello Nordic team,

I’m using the Mikroe nPM1300 PMIC Click Board (based on the Nordic nPM1300 PMIC) with an ESP32 over I²C to charge a Li-ion battery.

Setup details:

• Battery: 3.7 V nominal, 950 mAh Li-ion

• Configured charge current: 800 mA

• Termination voltage: 4.20 V

• Termination current: 20% of charge current (~160 mA)

• VBUS current limit: 1500 mA (set manually via I²C)

• NTC monitoring: Disabled

• Power source: 5 V adapter connected to VBUS

Issue:
The battery stops charging around 4.0 V, even though the termination voltage is set to 4.2 V. Once the battery voltage reaches ~4.0 V, the charging current drops close to zero, and charging does not continue to 4.2 V.

Questions:

1. Could any internal safety or thermal mechanism cause early termination near 4.0 V?

2. Does disabling NTC monitoring affect charging accuracy or limit the termination voltage?

3. Are there specific status bits or event registers I can read to determine why charging stops early?

4. Could voltage drops on VBUS or board-level limitation cause this behavior?

5. Are there additional parameters (such as recharge threshold or termination comparator accuracy) that could affect this?

Any guidance on ensuring proper full-charge behavior up to 4.2 V would be appreciated.

Thank you,

[mhni]

Hi,

During charging, the VBUS voltage is around 4.9 V, and after charging completes it rises back to 5.0 V.

I also read the BCHGERRREASON register but did not see any errors reported.

I tried reducing the charging current to 500 mA, but it didn’t affect the termination voltage.

When I set the VBUS current limit to the default 10%, the charging stops around 4.13 V.

So far, charging seems to stop normally without any error indication, but the termination happens earlier than the expected 4.2 V.

Yes, I do have the nPM1300-EK .

[Tomi Koskela]

Hello, 

Ok thanks for the information.

It would be good if you can try to replicate the setup on EK using the same 5V power adapter. Just to make sure there is nothing wrong with the connection or the adapter. Have you measured the 5V adapter output voltage with oscilloscope to see how stable it is? 

[mhni]

I have tested  using the nPM1300 EK and configured the charger using the nRF Connect for Desktop –   nPM PowerUP application with the following parameters:

• Charging current: 800 mA

• Termination voltage: 4.2 V

• Trickle/Fast charging threshold: 2.9 V

• Charging termination: 10% (default)

I also tested both configurations — with and without a 10 kΩ NTC thermistor .

The setup was powered using a 5 V adapter. During charging, the VBUS voltage is around 4.9 V, and after charging completes, it stabilizes at 5.0 V. The battery used is a Li-ion (3.7 V nominal, 950 mAh).

In both cases, the charging still completes around 4.13 V, instead of reaching the expected 4.2 V termination voltage.

[Tomi Koskela]

Hello,

In nPM PowerUP what does the battery status show? Does it go to constant voltage mode and what is the indicated battery voltage?

This is with nPM1300-EK and nPM PowerUP with the same settings you mentioned. Once the 4.2V is reached, the charger enters constant voltage mode and the charging current slowly drops from the set 800mA (in this case it has dropped to 550mA).

Thanks.

[mhni]

Hello,

Here are the screenshots from nPM PowerUP showing the battery status during and after charging with the nPM1300-EK.

• During charging, the battery voltage gradually rises until it reaches 4.2 V, and the charger enters constant voltage (CV) mode.
• In CV mode, the charging current slowly decreases from the set 800 mA (in this case, it dropped to around 73 mA) as the battery approaches full charge.

• Battery charging completed (V = 4.10 V, I = 0 mA, Fuel Gauge = 93.2%)