[engolling]

Yesterday night i let th TX4PRO power with UPS to see how long it last.
This morning the system was down, i then replug the power supply and just to see i measured the output voltage and i was surprised to have about 18V.
I the unplug the TX and let it charge again and now it's charged again(with blue led) and voltage return to 12V.
I don't undestand what happened, is it because the bateries were completely discharged ?

Hi laulau,

we need to do further investigation on this because this should never happen.
I assume you supply 12V DC with your PSU and you set the XL6009 DC/DC converter to about 11.8 V DC

Explanation what is the intended working principle when PSU is off
The battery voltage - range 8.4 - 6V DC gets boosted by the XL6009 to 11.8V which is set by the voltage divider on the module with the poti.
When the batteries run empty at some point the protection circuit switches off (at about 6V of the two 18650 in series) and stays off until you supply power to the batteries via the TP5100 charger module.
Then the current should be driven by the main path anyway and the batteries should be charging again.

Possible problems

Your PSU unit gets somehow disturbed because it is overloaded since the TX board and the TPS 5100 are consuming too much power. (2A in case of the TP5100).
Maybe you can repeat your test with a stronger PSU if this could be a problem.
Solutions: If you remove one of the too resistors "R100" (0,1Ohm) on the TP5100 you get 1A charging current.
This is a future recommendation anyway.

The protection circuit does not switch on again after the battery ran empty so you have a "pulsed engery" from the step down regulator of the TP5100 unbuffered at the XL6009 - this has an 220µF capacitor on its input - which should solve this but maybe it gets confused somehow.

You could check this by running the circuit without batteries.

Then we should be able to find out what is happening.

Regards, engolling

PS. A recommendation from my side - please avoid cells with "Fire" in the cell name. They mostly do not have over 1/3 of the rated capacity and they tend more to let its name become reality.