Laptop dies around 80%?

[pontiac4life]

I have an Acer 7739G with Windows 7 Ultimate and once fully charged and unplugged it will drop to 98% and I get about 25 minutes using it and around 80% it dies. Only does this while on battery. It acts as though it's a dead battery but Windows doesn't see that. It will power back on and dies within a minute. Any suggestion on why Windows doesn't know the battery is dead?

I've been told to calibrate it by totally discharge and fully recharge but I have done that and still dies at 80%

 

[MysticRyuujin]

And what are your power settings set to??

 

[MysticRyuujin]

Check this:
http://www.howtogeek.com/58109/how-to-lower-the-critical-battery-level-to-1-in-windows-7/