Where is the CMOS battery located in an Acer Revo One RL85 mini desktop PC?

The CMOS battery on my RL85 seems to have expired. I have studied many articles and pictures about how to open up the PC, which include images of the motherboard and the various other modules inside the PC. So far I have not found anything that says or shows where the battery is located or what type of battery it uses.

If anyone know how to replace the battery in an RL85, please will they give me advice on where the battery is, what type it is and tips on any special steps needed to replace it.

My RL85 has an i3 CPU, 4GB of RAM and a 500 GB HDD. Although there are two trays for extra drives, there is only one SATA socket for an extra drive. I don't know if this affects the location or type of battery.