It looks like the button battery drain investigation has progressed past any of my observations today being useful. So I'll just summarise it by saying:
- whether the Forma was in or out of the magnetic sleep case or whether the auto sleep/wake setting was on/off I had a reasonable battery drain rate of about 1%/hour whilst I was actually reading.
- Once the Forma was put into long term standby (by closing the sleep case cover) then the battery drained much faster - about 5-6%/hour.