For the moment, all phones on the market have a battery included
The best you can do is to choose a model which includes an improved battery, about 2000 mAH, able to support 10h of talking and browsing in 3G/4G mode
You can always buy an external battery, to supply you, whenever you don`t have the chance to plug your phone. External batteries can be 2000 mAH or even more
