The life blood of any mobile electronic device is the battery. The humble battery is often overlooked in many purchasing decisions, and yet it is the most important factor to consider. The iPad, which has a battery life of 10hrs, will suddenly be far less appealing if it were equipped with a 4-hour long battery. I used to own a Pioneer PDA which had a battery life of about 4 hours. It was a high-end PDA at that time. I was not able to make full use of all the features the PDA had, simply because the battery life was too short. I had to reserve the battery life for the more important uses, hence also limiting my use of the PDA.
The smart phone will not be quite so appealing had battery life improvements not kept pace with the computing power needed to run the smart phone. Putting it another way, the battery needed to power a smart phone for 3 days would probably be good enough to power a very basic phone today for 3 weeks. Now, that's a smart call (pun intended). We all need a phone to keep in touch, whereas the other functions in a smart phone are non-time critical (well, some people may argue with that...). The way I see it, perhaps phone manufacturers should start making solar-powered basic phones that can run indefinitely without having to recharge the battery. I will be the first to adopt it.