Battery performance

No, you can't just put any battery in there, it needs to be made for an iPhone. A 4200Mah battery isn't going to fit in there.

Also, the charging circuit is designed for the specific battery that is in there. Even if you could fit the battery in there (and you can't) it would not charge properly.

Visit an Apple retail store for a battery replacement. 

replacing the battery should be done by an Apple store or authorized service center.