More inspiration from the Grand Slam of a couple of weeks ago..
By the end of eight hours cycling on the Grand Slam my Samsung S2 battery was nearly dead, making it impossible to use the phone or text and got pretty close to losing the Strava recording of the day's ride.
Last week I bought a 2600mAh battery and replaced the stock standard 1600mAh and took it for an all day spin, with excellent results. Started at 7.30 am and finished at about 4pm and it still had mountains of juice in it (down to 65%).
If you use your phone for bike apps, I can recommend getting a bigger battery. There is a slight increase in the phone's bulk, but it is not significant.
On my S2 I've downloaded a program called Tasker...it's very powerful...not the most user friendly program..in fact you almost need to be a programmer to understand the full potential of it. I am not a programmer but have managed to setup a few tasks that are handy and one task at least helps me save some power. Tasker turns off my WIFI when I'm more than 100 metres away from my home (works on my GPS mark). You could also set it to turn off other programs etc that might run in the back ground. Tasker turns down all the volumes when I'm within 100 metres of work...saves me turning it down and back up every day. I also have it set to automatically open up my radio app, and set the volume to 10 for the headset when I plug in my headphones.
I have an Iphone4 which last days without recharging, when I run strava its good for 8 hours plus, certainly thinking about a battery upgrade for the longer rides now.
JB HiFi currently have an online special for the iPhone case-cover type extra batteries:
$19 and free delivery.
Hopefully that gets me more than 2 hours of phone use :)