thank you very much… Your ideas helped me to find, what was probably causing that problem… My secound name can be The Battery Destroyer… (and probably I can be happy that core module still works)… Why? I soldered cables to battery module (behind the first “minus” and after the third battery “plus”) - to get 4,5V. It worked, on the cables were 4,5V. But… I used relay modules as it is metioned above (simulating H bridge) and I used the power from battery module for operating the valve. For switching the bistable valve I just needed some short pulse, so I switched to True on the first relay and False on the second one and after 100ms I switch one of the relays back to opossite state. So, there was + and + or - and - on both cables… On the cables which were connected directly to the battery module. I am not sure if I am describing it correctly, but I have damaged three brand new rechargable batteries
At this moment I am using isolated power supply for the valve (three AA batteries)… but it is not so nice solution (use 4 AAA batteries + 3 AA batteries). Can some diode help to use it on the + cable from the battery module?
The image how to DON’T do that…
@hub.martin you asked me once, how I am skilled in electronics… So at this moment you can imagine