Dyson DC35 Charger

[najrao]

Quick enquiry: Can anyone put me wise on "What is with the 3 wire charger plug?" please. Supposed to feed 25.2 and 16.8V with common ground to the battery. Why?
Is it possible they use a tapped battery to feed the 16V brush motor? So the bottom four cells deplete faster, and need extra make-up charge? I must be wrong, of course.

Thanks.