When my iPhone 4S battery dies, why does it take so long to recharge?

Whenever my iPhone's battery completely drains, it takes a good 8 hours or so to "recharge" to the point where I can even turn it on again. My phone died this morning around 6 o'clock and has been plugged in since then. It is now 1 o'clock and it still can't turn on. When it will finally be able to turn on again, it will have around 15% battery life, but will then recharge quickly to 100%.Is this just an iPhone issue? Or is there something goofy with my phone or the way I charge it? (I plug it into the wall charger that came with the phone. That is about it.)

Could be a software issue, Backup everything through itunes, and I usually manually save my Photos and contacts just in case then restore the device through itunes it is real simple! If that does not work it is most likely a hardware problem with the phone or the charger you are using! Try charging through your PC/MAC or a different USB wall adapter, If that doesn't work get your phone checked out by a Apple genius or a third party certified apple repair centre, Your battery could be reaching the end of its life cycle.

You should never let it go all the way to 0. Then it takes a long time, start charging it up again when its still has a few % or more left and it won't take as long.