This article explains specifically changing the CMOS battery for Dell Precision 3431 desktops, but Dell desktops of similar model numbers will be very similar.
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3. Locate the CMOS battery, if possible. It is a coin-battery, a little bigger than a nickel. In the case of a Dell Precision 3431. It is underneath the additional video card. Similar models, such as the 3430 are likely to have the battery in a very similar location. This means the video card (if present) will need to be removed in order to access the battery.
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4. IF NO VIDEO CARD PRESENT, SKIP TO STEP 6. To remove the video card, locate the tab/latch on the back of the frame near the end of the video card. It has a blue rectangle on it, as shown in the picture. You’ll need to lift the end that is inside so that it unlatches. It is on hinges. Lift it so that is folds straight back, to get it out of the way. This will expose the frame-insert of the video card.
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7. Latch the new battery in place, plus-side up as shown in the picture for Step 6.
8.IF NO VIDEO CARD PRESENT, SKIP TO STEP 10. Realign the video card to click back into the same slot it came out of. It will click or pop back into place, but does not require a lot of effort. Just firm fingertip pressure. Note that the silver bracket that goes next to the frame has a tab that slides down into the gap between the motherboard (mobo) and the frame of the computer. The connector tab on the bottom of the card has notches to accommodate the edges and divisions of the blue housing that it slides into. The latch should easily move itself out of the way.
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10. Realign the tabs and notches on the removed side of the machine and the frame. The side should slide down onto the frame, approximately ½ to 1 1/2 to 3/4-inch back from the front of the machine. Once it settles into the notches, slide it toward the front of the machine until the remaining gap is closed and you hear the latch lock into place.
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