There have been threads about this, but I just wanted to summarize briefly for those encountering this error for the first time.

Scenario: Your SegaCD unit works, but it does not allow use of the memory. At some point in starting up your game disc, you get a black screen with white lettering that says something to the effect of: "Initialized by option command", "internal backup ram (backup ram cartridge) is unusable", "press button to reset". I didn't write it down before I fixed it, so I don't have the entire screen verbatim.

What should you do?
1)Reformat your Sega CD's internal memory: Restart your system. Instead of pushing 'start' at the initialization screen (which typically has a picture of Sonic and says 'press Start'), push the 'A' button on your controller. This will bring up the menu, which is the same menu you get if you put a music CD in your SegaCD instead of a game CD. There are options on the right side of the screen, the second from the top being 'memory'. I never knew what that did until now. You can select that option and then you will get another screen of options. From here, you can reformat your memory, copy items from memory, etc. You can try to copy files for games you've played now onto a SegaCD RAM cartridge, but in all likelihood, if you are getting that black screen of death, your saves are gone anyway. Sorry to be the one to tell you. Reformat the memory. It only takes a jiff. Now restart your system with your game and press start and see if you get that annoying black screen again.

If this solves your problem, then congratulations. If this problem occurs every time you restart your unit (forcing you to reformat every time), then keep reading.

2)Recharging your Sega CD's battery: Since the battery powering your SegaCD's memory is rechargeable, some sources recommend recharging that battery by either keeping the unit plugged in overnight, or even leaving the unit powered on for 6 hours. I would try just leaving the unit plugged in overnight before I left my system on for 6 hours. Repeat step 1), try your game again, and if you don't get the black screen of death, then your problem has been solved.

If this does not solve your problem, then the battery in your unit is probably dead. Keep reading.

3)Replace your Sega CD's battery: This type of operation is a bit more involved than any of the others. The instructions are here (digital press link!). I am a pretty poor technician, but I managed to do this with a soldering iron and a little luck. The battery you need is a 2016. I used a non-rechargable one. Perhaps I'll live to regret it, but you can probably get a rechargable 2016 pretty easily. It's a good 45-60 minute operation. I didn't remove the cables from the motherboard. I desoldered the battery contacts, removed them from the rechargable (which was a sloppy worrisome affair achieved by force), then reattached them to the motherboard. I then put a little piece of cardboard under the bottom contact, put in the 2016 letters up, secured the lot with electrical tape, and it all worked like a charm. I just wish someone had spelled out the other steps like this post does because I might not have had to do it, in retrospect, thus my inspiration to post this. I hope it is useful to all you Sega bitches!