Oh? Then that was a faulty board since the battery is directly in the CMOS holding voltage circuit pathway. Removing the battery is like cutting out a 1/2 inch piece out of wire. Do you happen to remember the make and model?Also note that even with the battery removed if the PSU was still connected and the switch was on I have seen the 5vsb cause it to hold cmos data.
It is important to remember motherboard engineers purposely use CMOS memory modules (around long before the PC) because they are volatile - EASY to reset. If they wanted user modifications to the BIOS information (the CMOS data) to be hard to reset, they would have chosen a different type memory module, like a EEPROM or the like.
That said, the power supply should never - as in NEVER EVER be left plugged in (or have the master switch on back set to on) when removing or inserting ANY hardware component on the motherboard.
That's an old wife's tale and does nothing. On old AT (before ATX) cases, the front panel power button was directly connected via a wiring harness back to the AT power supply and then, holding the button ensured the filter caps in the PSU were drained. The front panel power button did not connect to the AT motherboard.and draining power by holding down the power button for 30 seconds.
But on ATX cases, the front power button is just a "remote" switch to a "momentary circuit" on the ATX motherboard that controls (via the +5Vsb standby voltage) the ATX power supply. And a momentary circuit is one that accepts the initial input when the button is pressed, but totally ignores the button setting after that, until it is pressed again. So holding down the button on a momentary circuit does nothing but tire your finger.
With the care you took, I highly doubt any damage was done. But note whenever I handle and install new batteries, I always put a clean sock over my hand to avoid touching the battery with bare fingers as skin oils promote corrosion, and grab on to any dust that wanders too close.Hopefully I did not cause any damage with the CMOS battery reset; I was very diligent about removing it straight out and straight back in to minimize any contact that might cause a surge