On the other hand life could be extended from all these devices by using some of the heat produced by the circuitry and turning it back into power to charge the batteries.
I'm sure there are many many ways of turning heat into electricity.
And let face it, all these gadgets produce a lot of heat, so if that could be harnessed and put back into the battery, whilst it would not recharge them, it would extend the time you would get from a charge.
Perhaps this will come in time. It is a bit of a "No Brainer" as they say.
Well, there are some fundamental flaws with this idea. The reality is that somewhere around 10% to 20% of energy used in modern electronics goes into waste heat. So, even if you could recapture all of that and pipe it back into the system, the best you could do would be to increase the effective battery life by about 20%. However, simple physics tells us that you can't have any form of energy conversion that is 100% efficient, so don't expect to get anywhere near that.
That being said, the conversion of heat into usable energy is something of the Holy Grail for energy physicists and engineers. Currently, there are ways of doing this for large scale heat reservoirs (think of geothermal electricity plants) with the relatively high efficiency rating of 30-35%. Certain new designs that take advantage of extreme high temperature and pressure effects can get up to almost 50% efficiency.
For small scale thermal reservoirs (i.e. any iDevice, or even something as big as your car, which has a LOT more heat waste issues than any electronic device today), the primary way to convert heat to electricity is through use of the Peltier effect. In this case, this takes advantage of the fact that certain metal alloys, when connected to each other and kept at differing temperatures, will develop a voltage differential between them. Simply put, if you get metal A hot and keep metal B cold, you'll get power. This form of power conversion is limited, though. In cases where you can get fairly high heat differentials, you can get an efficiency of up to about 10%. But in instances when the heat differential is not as significant (think less than 100 degrees C difference between the temperatures of the two plates), the efficiency drops dramatically, even down to the 1%-2% range.
So, even if you could get a low temperature Peltier generator working with a "high" efficiency of 15% (which would be an incredible break through), you'd be able to recover 15% of the 10% to 20% of energy that goes into waste heat, giving you, at most, a 3% energy recovery. Weigh that against the potential increase in size, weight and cost of an iDevice that has such a heat recovery system. It would make far more sense for the engineers at Apple, at this point, to work toward reducing the amount of energy that gets lost in waste heat, rather than trying to recover it after it's been lost.
