I have a simple question regarding the new version of Wemos D1 Mini Pro v2.0 and specifically about its load sharing circuitry. Schematic is here :


Battery charger is TP4054 and there's a load sharing configuration based on P-MOSFET CJ2301.

My question is what happens if you do NOT connect any battery.

It seems that the charging LED faintly flashes, and positive voltage appears in positive battery terminal. Moreover, voltage appears in A0 and ADC input (provided that SJ1 is connected), while someone would expect a zero voltage there, since there's no battery.

Am I missing something here? Is there any way to fix this issue?

  • If you are not using battery, the SJ1 should be cut off so that A0 can be used as the input source to the ADC.
    – hcheung
    Commented Oct 6, 2023 at 15:10

1 Answer 1


I have test it and you are right. When you plug power into the USB connector with no battery connected to the Wemos D1 mini Pro v2.0.0 (provided BAT-A0 is connected) and I have got 1023, the maximum read into A0, when it should be 0.

I think a related problem is that when you are running with battery and you connect a charger into the USB port you can not read the battery voltage, you are getting always 1023, like if the battery was fully charged. So, you can use A0 to monitor battery voltage when discharging, but not when charging.

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