Thought I'd share my fix since I didn't find much in the Milltronics forum.

I have a 1999 mill running Centurion 6, don't have the SBC upgrade yet. I hadn't run the mill for a couple days, and when i went to verify a program everything was really slow. The mill machined fine yet.

I backed up my program and decided to try restarting it and then got a 'CMOS Battery Low Press F1 for Setup' screen. Pressing F1 took me to a setup page but my external keyboard didn't do anything after that, nor did the keys on the front panel. I did find a post that said to plug the keyboard directly to the motherboard inside the computer case. I did that and was eventually able to get back to the normal startup procedure however it couldn't find my saved programs.

The CMOS battery is enclosed in the Dallas Realtime Clock (RTC) chip. They are infamous for there replacement but mine was made in 96 and lasted 23 years. The problem is they are soldered in. There are plenty of tutorials elsewhere to guide you through your choice of R&R or modification to the chip by adding an external battery holder and a CR2032 battery. Not wanting to solder on the motherboard, I opted for adding a battery and holder.

You have to remove the motherboard to be able to work on the RTC. Most use a dremel to grind down to the battery terminals but I didn't want the debris all over the board. I found a guy who used a hacksaw blade to cut down to the terminals. That method and some files worked well. I also put some tape over the sockets to keep out any debris. They also make a socket that can be soldered in to make the RTC replaceable. If you want to go that route.

I reinstalled everything and set the date and time in the setup page. Plugged my keyboard back into the proper place on the front panel. Didn't have to reload or change any parameters!!
Did have to pull the video card and clean a couple pins as it wanted to cut out a couple times.

Hope this helps someone out in the future. Btw the old battery had 0.96 volts.

I was eager to get running again so I don't have a pick of the holder glued to the card support rail? Also this style holder seemed to be a little loose.