The biggest problem I hear and read is expected battery life versus the actual battery life. This misconception leads to a number of disgruntled purchasers. You can see this when you read product reviews. Of course this commentary is understandable especially when one does not grasp the concept of use in terms of battery life. The amount of battery life suggested on websites trying to sell you the latest and greatest is the best possible number. You can be assured of that little fact. What the websites tend to leave out are the guidelines to which they have tested the battery to conclude such a number. Therefore it might be difficult to judge how much life you will get from your use of the phone. Think about it like a laptop. The more programs (apps) installed & running, the slower the laptop (phone) runs because it has to use more resources and consequently the faster battery life dies. Recently I read some articles that discuss turning off random services on your smartphone to preserve battery life. Brilliant! Kill those tasks. Just like in a computer or laptop, hence the assimilation between the two.
If your smartphone is not getting the expected battery life that it used to get, you might want to look into these articles which provide tips and tricks to extending the life of your battery. A simple Google search on this subject will also yield a plethora of additional articles.