The phone's battery is ok, but just turn the screen's brightness to low
Hello, I had many of the same concerns about this phone before I purchased it, however, after having the phone and using it for a while as well as reading about the battery life of the lithium polymer battery, I'm confident it will last quite a while. Just note that the screen does take up A LOT of juice, therefore I have a widget to change the backlight to whatever percentage I want...normally at 10-15 unless brighter is needed...it's still pretty bright at zero. Also, there are a few games that really kill the battery, so make sure to be near an outlet if you want to play those for very long. But for the average person's usage...the phone's battery charge will last for a whole day...maybe needing to plug it in once during the day and at night if you use it heavily like I do. I've read that lithium polymer batteries actually work a little different than lithium ions; where they don't have a set number of charges, but if you keep the battery in good health, it should last a lot longer overall than the L-ions do. I normally don't even charge up to 100 because of a few articles I read about these new batteries. I usually charge it when it gets down to 15-20 and take it off in the 90s... it's a very fast charge too so you don't have to wait forever for it.
Best widget for setting the brightness I found is called... Brightness level
Also make sure to get Battery HD Pro... it tells you exactly how long you need to charge it for...tells the percentage of charge in the upper left hand corner of the device...and give you the temp and health of the battery. They have a free and pro version...not sure the difference but the pro version is cheap and very helpful.
Mine: AT&T HTC One X