On Mon, Dec 6, 2010 at 1:52 PM, Olin Lathrop wro= te: > > I took Martin's data and made a plot of it, which is attached. > > This says the phone has just a linear regulator between the USB power and > the LiIon battery. If there was a switcher, the current would not have > been > so completely flat from 4.8V on. If the iPhone does this then just 4 NiM= H > batteries driving the USB power will work, but leave a significant fracti= on > of the NiMH battery capacity unused. > Olin, Why would you say that? I suspect that there is some sort of a switching power supply inside the iPhone from various random articles I read on the Internet. Of course, they could be wrong. However, a threshold voltage of 1.15 volts/cell would not allow the pack to drop below 4.6 volts. At that voltage, the pack would be still be drained above 90% (if not 95%?) according to the chart here: http://www.eneloop.info/home/performance-details/discharge-current.html I think that's a reasonable voltage to cut off at. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .