iPhone 3GS switches off randomly after update to 5.0.1 I bought a used iPhone 3GS and the owner claims it worked fine with iOS 4.3.5.
When I came home, I reset all content and settings on iPhone.

Did I know that doing the reset would force me to upgrade to iOS 5.0.1!

Now that I have upgraded to iOS 5.0.1, the phone began to switch off randomly.
I can't recognize the pattern—it happens in different apps, with different intervals. The screen just goes blank, with a reflection of what was on it for a couple of seconds. 

Sometimes it reboots on its own, and sometimes it just switches off and sometimes it says the battery is too low to switch back on. But I know this isn't true! Funny enough, in a couple of minutes it would go from claimed low percentage back to 76%.

The only pattern I observe is it always switches off when I'm walking on a street, and works fine in the room. But it may be a coincidence.


Could the battery fail because of the cold or movement?  
Is this likely to be a software issue?
I tried jailbreaking and installing iOS 4.2, and the issue persisted so I concluded it's a hardware problem. After four months, I finally got the battery replaced, and the service guys told me there was a problem with the old battery's circuit.

The new battery works just fine.