Many battery-powered devices (i.e. cell phones, laptops, etc) require a calibration period before they start performing well. Note that this has nothing to do with a "memory effect" that old nickel cadmium batteries used to get. Calibration is needed to enable the device to properly gauge battery usage.
You can read all about it at
http://batteryuniversity.com/learn/a...ry_calibration
Many manufacturers recommend battery calibration on their devices, for example:
HP
Apple
Nook
When I first received my Android phone I was a bit disappointed at the battery life and when I started looking at the forums I found many other people threatening to return their phones because they weren't getting the battery life they expected. Turns out that everyone had only had their phones a few days and only done a few battery charges and therefore they hadn't calibrated the batteries properly. After doing a proper calibration the phones were much better and everyone calmed down.
So the basic message is that just because you've charged your device a couple of times and not received the expected amount of use, don't immediately blame the battery. Persevere a bit and do a couple of proper calibration's and you should find your battery life improving.