The CMOS is powered by the same battery that keeps the real time clock active. But the RTC needs a crystal to provide a time reference. If the crystal does not get power, then the time and date will be off. There was no intent to power the RTC and CMOS externally.. bad design! From that link I provided.. http://www.mcamafia.de/mcapage0/dsrework.htm
.. you can enlarge the image to note the features of the Dallas chip. Those two pins that are "missing" from the chip are tucked up over the chip for connection to the battery and crystal. You have to use precision in cutting away the epoxy, or the power circuit could be damaged. Yes, I did have a few 'bad repair jobs' when they were commonly used. The Dremel tool is the best to use, as you will note the change in sound when contacting metal instead of the epoxy.. and can retract from cutting.
The "internal" battery makeup was usually two small cells, some had only one small cell. Life was about 3 years or so before the battery died. No way the battery can be recharged, not designed for that!
The original battery may have been a mercury type, which is very dangerous to work with. Some were alkaline, the latest used Li-Ion batteries. Unloaded except for the test meter, even a "dead" battery may show good voltage.
If you can find a good replacement chip, work on that one to sever the internal battery lead and hot-glue a standard 3 volt battery atop it. Even a CR2016 battery should provide several years of service life. There are listings on eBay for the Dallas RTC chip. Some are listed as "new".. but buyer beware.
F@H.. to solve mankind's maladies.. in our lifetimes!