The battery of this phone seems fine. After having it for three days, it has been one and a half since last charging and now it shows 79%. I have realized that if you kill apps like crazy, many of them get automatically launched again, just to get killed again by software you have installed like Apollo Task Killer, etc. During the startup of an application it seems eating lots of power. I assume that this is due to eating up CPU resources in order to get running as fast as possible. This way, my phone had lasted for less than 8 hours on the first day after the first 100% charge.
Now, I kill reasonably those that I don't like when I start the phone and then I leave it as is. The battery seems now to last long.