Dell Precision M6700 with failed battery does not detect discrete GPU

I have a dell m6700 laptop with AMD M6000 graphics. Battery seems to be dead. Running on Direct AC power.

Couple of days ago, the laptop booted on Intel HD 4000, windows device manager saying GPU is disconnected - visible under hidden devices.

On running boot time Dell Diagnostics, it clearly said that the battery is not able to supply power to the GPU.

I removed the battery and still the laptop boots on Intel HD 4000. GPU missing. There have been couple of times when the bios did detect the GPU. Totally random.

Now the bios is only booting on Intel HD even on direct AC Power (battery removed). HDMI port does not work either, VGA is working. Weird.

Tested on two original dell AC adapters.

Any idea why the GPU won't start when on direct AC power?