I have a problem with my iphone 4s

Hi, I have a problem with my iphone 4s, this have iOS 8.4.1 the battery discharges alone and this and change recently, a technician told me I could be the source (or voltage regulator phone), as this is solved, because in Venezuela the crisis does not find solutions for the high cost, and besides everything is too expensive.

What is the solution? Please help.

iPhone 4S, iOS 8.4.1, .