Ok what I did is to remove the screws at the back of the YZXstudio ZY1270 with a PH00 screwdriver. In fact there were only 3 on them, one missing, and were barely loose. One of the copper cylindrical separators was a little bit unscrewed, so tightened it up, in case the bluetooth module pins (they are retractable) didn’t touch the pads. Set the serial update to 1 seconds and no bluetooth device is found by the smartphone right away, but if I use “hcitool scan” on linux it does find the “SPP-CA” device instantly. For the device to be found on the Galaxy S10 it takes about 40 seconds to find it and you have to press “Scan” twice on bt settings, so if you are eager you may think it’s not working.
Now what’s left is how to read the data from either the smartphone or Linux or Windows. Do I have to pair the bluetooth device or does the app just have a device selector? How can I do it?
EDITED: found how to do it. You have to pair the smartphone to “SPP-CA” with PIN 1234. Then I used the app Serial Bluetooth Terminal from Kai Morich. Then click on menu - Devices and choose the paired device. Then on Terminal tab click on connect icon and that’s it, will output the time, voltage and amperage. It has option to save, share and Log. Probably the way to save everything is to enable “Log”, otherwise after a while toasts the error:
Hint: Receive buffer truncated. Try ‘Settings -> Receive -> Buffer size’
You can click home button on phone to open other apps and it will continue working in the background.