The MT3608-based step-up arrives, I’ve tested today and it works fine from 2v. It’s good as the low quality batteries I have now could fail and, as I said, if the voltage from the batteries drops to 3v, XL6009-based step-up goes crazy and increase the voltage to more than 19v. Even when the good quality LG batteries arrives, It’s good to mantain a room, just in case.
You post put me in doubt: to charge the batteries I’m using 2 TP4056, both with 8206A MOSFET, 1 for each battery, as I said in the above schematic. It seems to work fine. Sometimes one battery needs to be recharged then this battery’s TP4056 red led turns on for few moments but soon it get off and blue light back. I guess, even the batteries is joined after the step-up, that it’s because the batteries quality.
But my doubt is: isn’t it redundance using TP4056 with 8206A MOSFET and a BMS board? Or maybe you said to completely rip off the TP4650 and to use the BMS board intead? I don’t know this BMS but I beleive it hasn’t indicator leds, for one to know when bettery is charging or when it’s charged. I know these LED are insuficient information but it’s better than nothing, I think. (The ideal is a LED or something like, to indicate how full charged (or empty) the batteries are. Do you know something like that? If exits something like that, I could use these BMS board instead of the TP4056… If I’m not boring you, what you think?