To start with, I have to tell you that all you have read about battery life is either BIASED, or tested with an unprofessional approach – all new batteries new some treatment, with prolonged charging being the least. Basically, the battery is not full when the phone says so, which is after about 2 hours. I recommend charging for at least 10 hours for the first few times. If you don’t do it, it will take longer for your battery to reach it’s full potential and it’s likely to behave badly in the future (worse than the properly treated one).
Having completed few of these cycles myself, I am confident my battery is fully charged and stores the maximum charge, and so I can tell you how long it lasts and what you can expect from it. However, bear in mind, that some of these are approximations are just… approximations :) Particularly the ones with low usage.
So to start with, I have to tell you that battery level indicator is not controlled by Sony Ericsson software, but by Symbian. This is very crucial. In most Sony Ericsson phones, the battery indicator underestimates the charge left in the battery e.g. if you use your phone heavily for long time, phone estimates battery drainage and when the battery level becomes low and you decide to leave the phone, after few mins the battery level goes back up, by 20, often 30%. Underestimation is a good thing though, as it protects you from losing contact from civilisation! :)
Symbian devices are different… In Symbian you don’t get the exact % of battery life. All you see is the battery level indicator on the home screen. Basically, that indicator says the battery is full for a very, very long time… And that is not true. I’m predicting it does it until the battery level is about 40%. Basically, when you notice your phone battery is not full, start saving, as you don’t have left what it says, but at most half of it.
Ok, so when it comes to actual battery life, in y opinion 1000mAh Lithium-Polymer battery Sony Ericsson has supplied us with is 100% sufficient. It will allow you to use your phone for about 2-3 days of medium use. When you are a type that uses the phone all the time, for taking pictures, calling, listening to music, browsing the internet, then you can expect a full day, but no more than that. Unless to use your phones extremely hardly, you shouldn’t run of of power during the day.
If you use your phone moderately (like me), the phone should last a day and a half (for example I don’t do much calling :P ). Nevertheless, I still recommend charging your phone daily overnight.
Anyway, you shouldn’t run of of power during the day, as most reviewers are suggesting. This is 100% black marketing. And if you really are an extreme user – you watch few movies a day, you shot a lot of videos and you play 3D games all the time, then yes, you will have to carry CPP-100 or a spare battery with you :P But that would be the case with ANY device I think.
P.S. Battery life is FAR better than iPhones. Sony Ericsson uses some (unknown to me) software tweaks to improve the battery life. I think everyone will agree they they are the market leader when it comes to battery life. And I believe there more to it than just high quality Lithium-Polymer batteries (everyone else uses Lithium-Ion). Just look at some mid-range Nokia device, and mid-range Sony Ericsson.. with same battery capacity and also very similar set of features. Sony Ericsson is FEW times better when it comes to battery life, but as I said, I don’t know the details of the tweaks they use :)
Nevertheless, once again, Sony Ericsson didn’t disappoint us when it comes to battery life :) (and not only with that ;) )
UPDATE: I just want to add that I am not a battery saver type, and all my settings, including screen brightness, have been at maximum all the time :)