There was a thread somewhere on these forums regarding the N900's ability to do some sort of negotiation for power with the USB bus it connects to, and most computers/hubs are able to work with this. But "dumb" power supplies (like a cigarette lighter adapter from your car to USB) don't have this ability...so the N900 never gets a negotiation response, and it never initiates recharging. Do some searching, might explain why you need a special charger (or a hacked one in your case) to charge from some other power source besides a computer.