Battery not Charging 100%

I bought Dell vostro 2520  3 days back...Right from day1 battery is not getting charged 100% it stops at 99% and even though it shows charging but there is no showing of 100%...

is it normal or please help me to resolve this problem

:emotion-22:also auto brightness adjustment where screen becomes dim when evr there is dark display.and vice versa with bright screen..help me to get rid of it