It depends on what "battery drains fast" means.  If it's running 30 minutes or less on battery, you'd be better off removing the battery from the system entirely.  End of life batteries can swell and present a physical and safety hazard to the system.  
My dell inspiron laptop ...battery drains fast...showld i plug in charger all the time and use? Pls help 
Inspiron 3000 laptop charging