The Obsession I motherboard (486) had two different manufacturers over the life of the product. The first motherboard was made by Sigma, and the other was manufactured by Teknor.
See the picture below for the actual location of the battery on the two motherboards.
The Sigma motherboard was the first board used in the Obsession I console. Sigma boards are identified by the length of the board taking up the entire depth of the console, front to back, and a soldered on battery on the left side next to the 8 sticks of RAM. If your board is a Sigma board, take note of the BIOS version on the chip with a shiny label marked, "AMIBIOS." Its CMOS battery is a 3.6v Lithium-ion barrel-shaped battery with solder mount leads. The ETC part number for Sigma board batteries is BT111.
The Teknor motherboard can be identified by its 2 sticks of RAM, being shorter than the depth of the console by about 2 inches, and having a disk battery at the back of the console. Its CMOS battery is a 3.6v Lithium-ion flat, silver, circular shaped 2-pin mount located near the rear of the 486 card sitting above. This battery can be pulled off of the board and replaced in the field, although care should be taken to lift it evenly off of the board from UNDER the black plastic, as the plastic is part of the battery. The ETC part number for Teknor boards is BT114.