The problems seem to come from the polyfuses installed in the board. There are two of them, and each one offers a different set of problems.
Fuse A: if your board has this fuse installed replace it with a Schottky rectifier diode right now. This fuse connects the +5V line with the positive battery terminal bypassing the li-ion charger, so if you install a battery, 5 volts will be applied directly to it, and the battery will eventually get overcharged and explode. Don't worry about the diode orientation: under the fuse there is a beautiful diode symbol in the PCB.
Fuse B: When operating the board from the li-ion battery, if this fuse is present you will find the battery voltage at the micro USB connector. This is not a problem if you have nothing connected to the micro USB port, but if you have something connected, like a turned off charger, power bank, computer, or something similar, your battery will be drained very fast by the device connected to the USB port. Again, the solution is to replace the fuse with a Schottky rectifier, oriented as the diode symbol under the fuse.
It is obvious diodes were the first, and the right idea. But for some unknown reason someone decided to replace the diodes with polyfuses and then, problems arose.
I'm using this board as experimental TNN gateway, with a 1.8 Ah li-ion battery and an small power supply I connect at day, and turn off by night. In this way the battery gets charged by day and powers the board during night without getting discharged by the current flowing by the switched off power supply. With both polyfuses replaced by Schottky rectifier diodes, it works just nice.
Miguel A. Vallejo, EA4EOZ
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