[minus365]

A good tip for battery life, which I found here back in December (The thread is probably well buried by now though!) is to fully charge the phone to 100%, unplug and then use it till the battery is down to very low - below about 10%, recharge fully again, and repeat.....
I was having similar 'problems' that you describe at the time, and tried this tip... it kind of resets and 'trains' the battery!
I'm not a heavy user of the phone, but I do let apps update as needed, etc - I like them have full functionality all the time! I can now get upto about 48 hours between charges, but that of course will vary with use! :)
Hope this helps.....

This is not needed with Lithium ion (Li-on) batteries.

Wiki:
Battery life
Rechargeable battery life is often stated in number of charge cycles, but depth of discharge is usually not explicitly stated. Apple Inc. clarify that a charge cycle means using all the battery's capacity, but not necessarily by full charge and discharge; e.g., using half the charge of a fully charged battery, charging it, and then using the same amount of charge again count as a single charge cycle.
Lithium-ion battery - Wikipedia, the free encyclopedia

[johnskrilla]

Simple example is if you stop background task for whatsapp you won't get notifications when you exit the app. You will have to open the app to receive messages. Now did you get what background task is?

ok cool thanks..

[edwardng88]

Yes I'm facing the same problem with 925, when reset or restart 60-70% suddenly gone.

[Munter2]

This is not needed with Lithium ion (Li-on) batteries.

Wiki:
Battery life
Rechargeable battery life is often stated in number of charge cycles, but depth of discharge is usually not explicitly stated. Apple Inc. clarify that a charge cycle means using all the battery's capacity, but not necessarily by full charge and discharge; e.g., using half the charge of a fully charged battery, charging it, and then using the same amount of charge again count as a single charge cycle.
Lithium-ion battery - Wikipedia, the free encyclopedia

Thank you for bringing that up. The guys who are encouraging draining this phone's battery below 10 percent are helping others kill their batteries. Keeping the charge above 50 percent as much as possible is how to be kind to a lithium-ion battery.

[jorgetal]

One day i had the same problem on my 830:(

[Kristina Navickaite-Momchilova]

To check if there is apps running in the background , go to settings - battery saver - usage and then you can check each one separately.

[ramvigneshkumar]

i'm also facing the same issue have you got the solution??