Hello guys. I'm experiencing this same issue since this morning. I found my phone turned off in my pocket, but didn't pay too much attention to it. Later, I was Skyping via 3G for about half hour and suddenly audio started to fade, and when I checked my phone, signal whas showing the simbol Ø. After rebooting foud out that battery was dying, so connected just to say goodbye and went to lunch.
After lunchtime, looked at my phone and realized that battery has been misteriously recharging. Plugged my phone at the office, and rebooted a couple of times. Below you will see the charging timeline, after removing and reinserting the battery, level seems to increase (see last bit)
What's courious is that battery level seems to drop a little after booting the phone. After reading this thread assumed that I need to replace my battery (got my phone a little over one year ago), even if it doesn't "spin" when in the table, and both sides are completely flat, but I think it was interesting to show this to you guys.
For the last two months my battery has been taking a little too much, because signal here is really low, and I need to keep my phone plugged to my office laptop all the time.
Regards,
Sebastián