If I use my HTC Desire for Google Navigation in the car, with the phone plugged into a USB power adaptor for the cigarette lighter socket with the cable that was supplied with the phone, the battery still runs down. A dialogue pops up when the battery is getting low saying words to the effect that the phone is using more power than is coming in via the charging cable. I notice that the phone distinguishes between being charged on AC and being charged by USB. In Settings->About Phone->Battery it says, "Charging (USB)" or "Charging (AC)". I believe that charging from a PC USB socket is limited to <500ma by the USB spec. I guess the phone knows that it can draw more current when connected to the AC charger. The supplied AC charger must have some way to tell the phone that it is connected. Perhaps it communicates with the phone via the USB data lines, or something simpler like the data lines being shorted together? The USB power adaptor I have in my car can source 1A. If I can work out how to convince the phone to switch to "Charging (AC)" mode then perhaps it can do Google Navigation and charge the battery at the same time...? Does anyone know for sure how the AC adaptor identifies itself to the phone? Rob.