battery of iphone 4 is charging very fast and draining fast

hi

my iphone 4 is in extended warranty now,

this phone has iOS 6.0 at the time of purchase, after every mandatory update ( iOS updation done by inspire only every time) , phone became more and more slower,

battery drained faster,

apps crashing frequently,

screen freezes often,

after so many rounds to apple service center nagpur they finally change battery 18 days back.

problem is still same,

phone is still slow as before,

apps are still crashing,

new thing is

BATTERY got fully charged in 1 hr 20 mins (from 0 to 100%)

and drained almost in 3 hrs

i have to charge my phone at-least thrice a day or sometimes 4 times a day.

now what to do