My Dell XPS 13 (9343) has been non-operational for the better part of 4 months now. This is mostly my fault, as I was scared to bring it in for repairs, fearing a sky-high bill (my warranty expired in early 2016). I will describe the issue and I hope someone may have had my problem before or could offer some advice:

When the laptop is powered on, a yellow light facing the user (usually white to signal start-up) comes on and flashes intermittently. I don't know how to describe the noise that begins to sound other than 'an alarm'. Dell says it is a beep, I say a tornado is about to hit town. Whilst plugging my precious ear drums against this maelstrom, I count 5 beeps (months ago, when the problem had begun there were only 3 beeps *System board failure, says Dell online guide*). The guide I found online shows that this means a CMOS battery failure. 

Does this mean that I need to replace the motherboard? Or simply the CMOS battery? And since my warranty has expired, am I free to safely open the device and replace these myself?

Thanks for the help!