User Activity

My phone's battery life has been to short now a days first it was covering 1 day easily but now it has been reduced to 8 to 10 hours only and I am not extensively using it so what is this problem and its solution.
Any of the sensor are not working on my device what can I do now and the battery working capacity has also decreased all at once first it could give a 24 hour standby level and now it has decreased to maximum 13 hour on the standby now what is that p...