Any interest for custom PCB for 4 bay USB charger?

So all of my generic 4 bay 18650 USB chargers overcharge my cells. Not by much, but enough to saturate my battery of Lii-500's. Seems hard to wake up cells for 0 V too. This got me thinking, perhaps make a custom PCB for it with slightly added functionality, possibility to change charging current and more indication if one would be willing to drill a new hole for LEDs and sort out real TP4056 which are within spec.

They are dirt cheap and the spings can come undone and by the time the PCB is finished and components bought, it might be cheaper to buy a more full-featured one, though the UVLO seems to be a "feature" for manufacturers but not to me.

Lii-500 reverse engineering is ongoing in the meantime

Would anyone be interested in it and if yes, what functionality would you like?

Interesting idea. I would recommend going with the TP5100. If you're getting the pcb done and needing all the components anyways, you can get the 5100's from LCSC for $0.48/unit or less (depending on quantity; down to $0.30 for 500).
Using the 5100 would allow you to use a much wider range of voltage input. So as long as the power source is 8 - 20V and can supply at least 5A, then it'd work nicely.
Datasheet: http://www.microlab.info/wp-content/uploads/sites/5/2018/06/TP5100-EN-autotranslated.pdf

Use the MCU to control the amp output, and if you go with an ESP32 or ESP8266, you could even make an app so one could monitor it on a tablet/phone, which could greatly increase functionality. Like showing live charging/discharging graphs for each cell.

I'm with Korishan on using a different chip. I was looking into this myself last week, more to just see what it would take than seriously designing one, and there are a number of other charge controller chips out there with good features for very reasonable costs.
Considering you can get TP4056 boards for roughly $0.25/ea off eBay or $1/ea on Amazon I'd go for specialized features already mentioned, like a monitoring ap you can have on your phone, notifications when charging is done, and customized charging profiles that can be configured in ap.

Sounds like a fun project!

Church1182 said:

like a monitoring ap you can have on your phone, notifications when charging is done, and customized charging profiles that can be configured in ap.

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The Lii-500 will have Bluetooth but someone else needs to write said app. It will just be console output dump of data.
This one I'm only using to precharge my batteries since my battery of Li-500's is the limiting factor, so I won't spend too much nor add real features.

Korishan said:

Interesting idea. I would recommend going with the TP5100.

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That datasheet was really bad, but they do mention ticke-pre-charge below 1.2 V. Not sure that would mean 0-1.2 V. Does anyone own a TP5100 based charger and can test it? Apart from that, looks like everything I need.