USB power versus batteries
I notice that when Twine is plugged into a wall charger the voltage shown on the Twine web site drops about 0.15v. On mine, it shows 2.80v on batteries, and 2.65v on charger. I wouldn't have expected that, but it may be due to
twine's internal regulation of the 5v from the charger. Anyway, it's one way to tell if Twine is plugged in.