Santi12008, You do not state what device you have or how old. Your devices battery may be near its end of life or faulty. Maybe replace the battery and use the information below, tips and tricks on extending battery life and usage. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
http://www.digitaltrends.com/mobile/how-to-make-your-cell-phone-battery-last-longer/
http://www.makeuseof.com/tag/how-to-make-your-phones-battery-last-longer-and-hold-more-juice/
http://www.pcadvisor.co.uk/how-to/mobile-phone/how-improve-smartphone-battery-life-facebook-myths-3284240/