Yes, your CMOS battery has recharged itself.
Yes, your CMOS battery has recharged itself.
This situation seems strange at first, but it makes sense once you look closer. The battery might have held up well despite the initial issues. The system initially reported problems with the time and date, which could be due to a temporary glitch or incorrect settings. After adjusting the time/date in the Control Panel, everything functioned normally. It’s likely the CR2032 battery was still present and working properly.
It seems the configuration was preserved since power remained from the outlet until you disconnected the cable, which then re-established the CMOS.
The motherboard does not recharge a CMOS battery. It is not designed to be rechargeable. The power for the battery comes from somewhere else, but there isn’t a direct source feeding it. Likely the initial voltage reading was incorrect due to a faulty connection. Once you remove the battery and unplug it, the capacitors in the PSU and board can retain charge for an extended period. It may take hours, days, or even weeks for a BIOS chip to discharge them fully. EDIT: It’s advised to press the power button when clearing CMOS and unplugged from the wall. Concerning timing, even with a fresh battery on a new board, the real-time clock chip can malfunction. I’ve noticed this on several older boards that are no longer available. May they be in peace.
I have three boards from this period, and one isn't functioning properly. It has some caps that leaked, so I believe it needs a soak in isopropyl alcohol and a cap replacement. That might resolve the issue. I'm not familiar with such a clock battery setup. The PSU includes decent filter caps—power lights remain on briefly before fading out once the system powers down and fans stop. It's worth checking if this is connected to it. I haven't unplugged anything for more than a few days at a time.