I have identified a process "android.hardware.nfc@1.1-service" occasionallly using up one cpu core (top in termux) and draining the battery then. Turning off nfc heals the problem. After reenabling nfc cpu usage stays down. I can see this happen every one or two days.
For the time being it might be best to keep nfc disabled until one needs it. Bug ticket @PC already opened.
