I have been using my iPhone 4 for more than a year already. However, only this 1 month ago, I notice my battery drops much quicker than it normally does. When I arrive in the office in the morning, my battery will be around 95%. However, by the end of the day around 6pm, it would dropped to below 40%. This is when I do not even use the phone much. Maybe one or two 1 minute calls. A little bit of SMS and some checking of the status. I normally already have a lot of the phone function turned off such as Bluetooth, 3G and Edge. It took me some time to find out that WiFi is the one causing this problem.
When I turned off WiFi, by the end of the day, I would still have around 80% of battery juice left. That is a whole lot of difference. And the thing is, this does not happen when I am at home during the weekends. I can leave my WiFi on the whole day and battery will not suck that much. Next, I leave my WiFi service running in my iPhone but do not let it connect to my office’s WiFi. Just go to settings and network then forget all the saved networks. After testing this for a few days, I notice my battery does not get sucked like before. It stays at around 80% by the end of the day. This can confirm that somehow my office’s wifi is causing the problem. My best guestimation is that some sort of malware or virus is running in my network scanning for connections and probing all ports. So when my phone is connected, it will reply with all the relevant “replies”. Thus draining the battery while doing so.
So next time when your iPhone battery juice is moving faster than it should, don’t put the blame on Apple first. Try checking to see if your WiFi network is causing it.