If you’re constantly using the Facebook or WhatsApp app on your iPhone, iPad, or iPod touch, then that may be the reason the battery dies so fast on your device. A German iOS developer recently conducted a test of his iPhone’s CPU using developer tool Instruments. Using the Instruments tool, he was able to check which processes are consuming the most CPU time. It turned out that the Facebook app was using most of the CPU time within the system. According to the developer, the Facebook app, even when closed by pressing the home button, is active in the background the whole time. The developer also found out that the app “wakes up  every few minutes, does something for 10 second and sleeps again,” which causes the battery to drain fast while the app consumes CPU time.
The German iOS developer also found out that WhatsApp consumes a lot battery. WhatsApp after your close it by pressing the home button, it stays active for 10 minutes communicating to its server instead of using iOS’s native push notifications. Here’s the dev explaining it:
WhatsApp for example. When it seems like it’s terminated it’s actually running exactly those allowed 10 minutes and continues to communicate directly with it’s server instead of using iOS’ push notifications. That’s draining more battery, of course.
So if you are getting a message in this 10 minute timeframe and open WhatsApp, this 10 minute period starts again. That means if you are getting lots of messages it could happen that WhatsApp is running the whole day.
To fix this issue you have two options. For Facebook, you can delete the app and use Facebook on Safari. But to fix it on both apps, all you need to do is completely close the apps by double tapping the home button, holding the app until it jiggle then hitting the minus sign to close it.
(Source –Â blog.hagga.net)