Having just upgraded from the first iPhone to the 3GS I have to say I am disappointed with the battery life on the new handset, it's certainly not the improvement I was expecting from reviews. With Wi-Fi and location services turned off and very light usage I can get just about 2 days out of it, normal use sees it being recharged every night which is inferior to the old model. I was contemplating returning it to O2 but before I did that I wanted to know if there are any standard tests to see if my battery is that much worse than normal, e.g. the phone plays a movie for 5.5 hours at 75% brightness or play music through headphones for 9 hours from full charge etc. Any thoughts? Reviews also seemed to suggest there was a better battery meter in this model but I haven't seen it, 20% charge remaining still seems to mean run for a recarger, not you have 20% of the usage time you would get from a full charge left.
Any given program will expand to fill available memory.