small cover at the back

what is this cover near the battery that has two screws holding it. I open it and there really noting there. does anyone know what its for?

 

From the description you are giving, mentioning only one cover, it means you have an AAO A series (A110 or A150) model with a 8.9" screen.

The bay underneath that cover is meant to contain the Mini-PCIe based 3G modem, on the 3G enabled A series models. Instead of having different bottom casings for the Non-3G enabled models, and the 3G enabled models, Acer saves money by using the same bottom casings. The motherboard on the 3G enabled models contains an extra Mini-PCIe connector which can be accessed from the that bay and which holds the 3G modemcard. The 3G enabled models also have a phone-SIM card holder on the motherboard, which fits with the slit behind the battery in the batterybay.

The non-3G enabled models also have this slit in the batterybay, but doesn't contain neither the simcard holder, or the extra mini-PCIe card connector on the motherboard. You can mod the motherboard on those models, just as aspireoneuser forum regular "jerryt" has done. He has even described the complete procedure in detail here on the forum, down in the hacking and modding section.

 

thanks for the explanation. I understand now. The modding seems tempting.