I have a Samsung Galaxy S2 and this past week whenever I turn on the wifi and start browsing the internet or using web-based apps, the phone immediately shuts off and will not turn on unless being charged. My battery is never that low when I turn on the wifi so I don't understand why it shuts down so fast (within a minute usually, but it has been worsening). This is also the case for 4g (which I hardly use). I first noticed it with 4g and 3g so have just been avoiding turning it on but when I do, no matter what my battery life, the phone immediately shuts down, without playing the shut down sound like it usually does when the battery dies. I can use wifi or 4g when my phone is plugged into the charger, if that helps diagnose the problem at all. Without wifi on, my phone holds a good charge, and even before this started with wifi on, I could use it for internet access for a good while before my battery started dying. I haven't tried a new battery because I have read about people with similar problems who replace the battery and it not helping. If someone can point me in the direction of what I need to do to fix this, I would really appreciate it. Thanks!