Battery level suddenly drops from 35% to 7% , please help me

[shab_2008]

Hello everyone,
About one month ago, I bought a ' Lenovo IdeaPad S510p '. Since that time, I had not faced with any problem until a few days ago that I realized the battery level suddenly dropped from 35 %to 7%. Another problem that I encountered was that the battery wasn't charged completely, and while charging, it stuck at 99%.
Regarding this description, what's your idea about this issue, and what do you recommend for solving my problem ?

Thanks in advance.

 

[plaintuts]

You may have a faulty battery.