How to replace the dreamcast battery

Can some one tell me how to, or point me to a rough guide on replacing the dreamcast battery? Ie where is it? What type is it? And does it need to be replaced by a rechargable one? I read through the other post regarding the dreamcast battery but it was no use.
There is no battery in the way the saturn had.

Just some kind of accumulator for holding your bios settings for a few months. It recharges every time your dc is switched on. And no I have no idea how to replace it if it's broken.
I just opened up my Dreamcast and noticed that the controller board had a large purple disc sticking up from it (presumabley the battery). I saw that a piece od metal was protruding out next to it as if it had been connected to it and come loose some how. So I've seletaped it back on. Now I'm waiting to see if it works again :)
If it turns out you do need to replace the battery, I believe it to be soldered to that board and I have never seen a replacement for sale. Anyone know a site that has them or can you just replace that board?