[Microbit-Python] Microbit operating voltage range

[fresh.bread]

Perhaps a bit off topic, being a general hardware question, but I can't 
seem to find the appropriate forum to ask the question, but does anyone 
know what the Microbit's operating voltage range is.

1. I have seen it suggested that taking it above 3V isn't a good idea, 
is that true?
2.  Has anyone measured the minimum operating, I coupled it to a pair of 
rechargeable NiMH  cells,  these were freshly charged and putting out 
2.6V. My patience ran out before the cells.. Will it work off 2.4v (i.e 
a pair of tired NiMH cells)