My mobile phone battery started to run out of charge quickly. What might be the reason for that?

Some of your apps might not be updated. So update your apps. If problem is there still reinstall all the apps which has not been used regularly.

Also do a network reset.

Problem in Your Battery. other reason your charger of run out from electronic switch. 

Instagram and snapchat will Drain battery faster. 

battery expire so i will replace it

maybe the batty is good enough or one of the panel is good again 

Your phone probably is running alot of apps in the background or your data is left on when your not using any apps at all.

there must be2 reason for that 1 Your charger might be not working properly u should change you chager. 

2 May be it is the problem of your battery if u charge your battery more than% and do not unplug your charger than your battery is gone you have to change the battery 

if ur mobile is running out of charge quickly.. its probably the issue with ur battery... 

Well if you are talking about smartphones you should know that smartphones come with a lot of features that a simple phone does not have. like wifi, camera, better resolution. and much more to utilize your need 

example: when you put 4100mah battery into a simple phone when will last maybe for 6 or 7 days but the same battery for the smartphone will last maybe for 2 days without intensive use because of smartphone use so much more application as compared to a simple phone can.

Thanks.

There is many reason to that . Depending on the type of mobile phone(mobile class : high class) the performance of the mobile (high performance), fabricant the mobile and the starting configuration made on the mobile phone  it could runs  application in  background, also when the mobile used  "mobile data" features it could use more power than usuall. as we can see there is multiple reason to that  but  to get the  right the question you must askyourself are:

- Does my mobile has a lot of  application installed?

- is the feature  runs in background enabled?

- what  am i doing now  with mobile (video, photo, mobile data) 

- what my mobile is age? (for  how long have it been used)

to optimize the  use of battery "battery save" software are installed to controlled, detected  application which consume more power than usual and let the user  take  action to keep or close the application, and then free some memory space, optimize battery is used  for a long term  and only  critic  application such as dialing or message ...

Change the Battery. This is the only solution for this issue.