This machine doesn’t rely on a CMOS battery judging from the teardown. These devices typically rely on a small reserve capacitor near the Flash ROM or have a dedicated battery line to do the job the CMOS battery would normally be used for.

If you want to get the CMOS RAM to save again, you will either need to find the capacitor(s) that provide power to the CMOS RAM, or replace the battery.

That being said, the capacitor is usually fine and it’s typically due to a older battery. However, you may as well double check the board and 100% rule it out.