Testing CMOS Batteries CR2032

[Executioner]

This is puzzling to me. I bought 2 used Dell laptops cheap because when powered on, the Dell logo would briefly be displayed and then the laptop would shot off.

After I disassemble the laptop, one of the checks I do is the CMOS battery using a Fluke DMM. The CMOS battery shows 2.9 volts. So I continue to trouble shoot, but this time I decided to take the CMOS battery out. I used this battery tester https://www.ztsinc.com/mbt1.html and the CMOS battery is dead. Not even 1 bar on the tester. So why would the CMOS battery indicate voltage on the Fluke DMM?

Anyway, I replaced them and the laptop now works fine. I know my Fluke meter works fine, because I checked it with another Fluke meter with the same results. Is this because there is still some voltage in the battery, and if I left it on the DMM, would the voltage gradually drop?

[FlyingPenguin]

I've seen dead CMOS batteries witn even higher voltages. Voltage alone means little. You want to put rhe battery under load, and then check the voltage, which is what a tester does.

If you don't have a tester, then I would throw out any battery that comes up less than 3.1 volts on a digital multimeter. A brand new CR2032 will generally read around 3.2 volts without any load on it.

[Executioner]

I still have the battery, and what I did was to test it again with the Fluke DMM while I watch the readings. They continue to decrease while I was testing it. So I'll have to remember this next time when checking them. If they start to drop in voltage, they probably need to be replaced.