I think it is partly related to the charger you used, and which power outlet/surge protector you may be connecting to. I noticed one outlet at a relatives house was taking the better part of a 24 hour day to complete a charge. Electricity does a lot of really weird things.
Also, try using "Battery Doctor Pro" from the iOS App Store. It gives you a lot of tips on how better to manage your iOS device batteries.
If you think your battery performance is taking a big, sudden, and unexplained hit, then it might be related to a recent iOS OTA upgrade/update. Usually, this can be fixed with an iTunes restore with a new download/install of the latest version of iOS. Sometimes, the iOS battery firmware just works better after upgrading via USB instead of OTA.