iPhone shut off when battery full?

Hello,

I was just on a call when my iPhone shut down completely, and I am unable to turn it back on again. The obvious reason why is that the battery has run out, but the battery meter was showing as being full, and I had only been on the call for about 30 seconds. I won't be able to connect it to my mac 'til I get home from work later, so in the meantime I was wondering if this had happened to anyone else? And also to see if anyone can advise why this might have happened, and what I can do to prevent it happening in the future?

Thanks in advance.