MacBook Pro Early 2011 (8,1) Battery Not Recognised/Fans Full Speed - SMC Reset does not fix

My Early 2011 Macbook Pro (13") started behaving erratically. Fans full speed and noticed CPU was running high caused by a process "powerd"

Eventually it powered down and would not restart. When pressing the power button the SIL would flash once and then nothing.

I tried reseting SMC and the same thing happens.

However, (after franticly googling), I was able to find a method to get it to boot up:

If I remove the Mag Power connector and then press the power button down for 10 seconds and then re-attach the Mag Power connector, then release the power button, and then press the power button again, it boots up.

As soon as it starts to boot the fan is at full speed and continues once the OS comes up. There is no battery indicator on the menu bar, and when checking System Information there is no battery information on the power section. The LED on the Mag Connector is always off and the battery level indicator on the side of the Macbook is also off when the button next to it is pressed.

I can restart the Macbook once in this state. However, if I try resetting SMC again it will not boot. Back to the previous state of SIL flashes once and then nothing. To get it back up again I have to use the method described above.

Other things I have tried included physically disconnecting and then, after a several minutes, reconnecting the battery and resetting PRAM. CoconutBattery app simply states that the battery is "unknown" and that there is no power adapter found.

I am in the process of ordering another battery, but concerned that the Macbook cannot even recognise there is a bad battery in there and also that the the SMC reset seems to make matters worse.

Why does the method of removing the Mag Connector and pressing the power button for 10 seconds bring it back to life?

I'd appreciate any suggestions as to what to do next.

Thanks,

agm1000