Anilam used four different motherboards,two with replaceable batteries,two without.
The ones without replaceable batteries used a real time clock{RTC} usually DALLAS but in my case ODIN.This is a package not a chip containing a chip a Xtal and a battery.If it was in a plug in base no problem. A new RTC can be bought via auction sites for less than $10.They are available from a US components supplier at $23.
The difficulty is the old RTC has to be desoldered from the motherboard and the new one fitted.This is almost impossible.
The solution :- cut into the package until you find the old battery connections at pins 16 and 20 solder on a battery holder and use something like a CR2032 3volt battery piggybacked onto the package.CMOS now works and motherboard works.You may have to boot the first time with a boot disk,I used a DOS 6.2 disk 1 .
NO expensive upgrade and cost me less than $10.
When I can work out how to do it I will post a link to a site that will explain with photos how to do this.