Based on this question I created the following circuit: tp4056_mt3608_ups Since I made some (component) changes, first I would like to have a validation of the circuit for long-term usage (and some improvements).

Used components (different from linked circuit):

  • 1N5822 diode
  • AO3401 P-channel mosfet
  • 3.7V 2600mAh 9.62Wh (protected) Li-Po battery (from another project)
  • Added a ceramic capacitor and a toggle switch (I hope to the right position)

I made this circuit as a battery backup solution, so 99.9% of the time it will be powered externally, but I don’t want the Pi to shutdown when there is a power outage.

Here comes my question #1: do Li-Po or Li-Ion batteries serve long time if I connect them to a TP4056 charger constantly?

Currently I’m testing with a Pi 3b+, but I later want to upgrade to a Pi 4. The circuit works fine when there’s external power, but I have issues when I switch to battery powered mode. During boot, the Pi shuts down. If I’m right, the battery protection in the charger module kicks in and saves the battery from over-discharge. When this happens I get no voltage from the out pins. So I made this modification:

enter image description here

So I connected the battery directly to the mosfet, because the battery itself has a protection circuit. With this modification I almost get to the desktop, but a little before that I get a reboot. If I turn off the external power when the Pi is in idle state, the circuit works until I open an app and it reboots.

I don’t know the C rating of my battery unfortunately, got it from China. But I have a linear bench power supply. Question #2: Is it safe to connect it to the TP4056 as a battery replacement to test how much current does the boost converter needs in battery mode?

#3: I’m thinking about buying a reliable 18650 Li-Ion battery with a high current rate. Do you think it will solve my problem?

As an alternative solution I just connected another charger module in parallel like this (with a second battery), but I got weird things happening like they randomly showed ‘charging-done’ state when they weren’t full. After reconnecting the external power they started charging again. So I would stick with one charger/battery if I can.

My question #4: is there a dc-dc boost converter which has higher efficiency than the MT3608 when using batteries? Also I don’t really need the adjustable output, and actually that potentiometer looks like a cheap component which is not reliable at all. Just need a stable 5V output.

Thank you for your help and answers!