Why does my phone die the second it activates low battery mode?

[AC Question]

My phone just died as it displayed the low battery mode warning, I'm not sure what percentage it had. So I put it on charge and it got up to 10% before I turned it on. Then when I turned it on it had 55% battery life?? I took it off charge and I've been using it for about 20 minutes and the battery has only gone down by 3%. It's impossible to go from dead to 55% in less than 10 minutes and I can't just have my phone dying on me when it fells like it.

 

[sethyboy]

It could be that your battery is going bad in some way. What device is this, exactly?