The button battery on a mboard usually lasts at least 5 years, unless it's the rare case it has leaked and failed.
The + on the button battery should be upwards, on the top, where you can see it. If you have that backwards the cmos behaves as if the battery is dead.
Sometimes the contacts that are supposed to touch the battery get bent while removing the battery such that they no longer touch the battery when you install one again. Good lighting and possibly a magnifying glass will reveal whether that is your case.
There is one on the side (+ polarity), one under the battery (- polarity).
Rarely, there will be corrosion deposits on one or both contacts - clean it or them off if you see that.
Some out of the ordinary circumstances can cause the computer to go into the bios Setup while booting, or prompt you to do that, but in that case you don't get the bad checksum error or similar, and the time and date are not reset to defaults.
The QVL list on the mboard or brand name system manufacturer's web site often has a limited number of modules listed, and may be outdated as well.
The ram manufacturers and major ram distributors have the most up to date info about which ram modules work in your mboard for sure (are compatible).
In this case, you can easily go to the crucial web site, select Find Your Product - Find the Right Memory
which takes you to the ram configurator page
where you plug in your brand and model to reveal the list of their modules that have ID strings that work in your mboard:
If the ID string on the modules you have are on that list, the ram is compatible with your mboard for sure.
If it isn't, it MIGHT work, but there's no way of knowing for sure until you try it.
You should always check whether a particular module or module set ID string is compatible with your model (is in a list of modules that work for sure) BEFORE you buy it.