I bought a brand new computer mainboard on May 3rd 2024. It’s a B550 AORUS ELITE AX V2 (Rev. 1.3). In July of 2026 the CMOS battery was completely dead. Instead of simply replacing it, I investigated the cause of this, because CMOS batteries shouldn’t die after just over 2 years.
Setup
To figure out how long I can expect a battery to last, you have to measure the power consumption while its connected and check that against the energy capacity of the battery.
To do that, I simply connected a Nordic Power Profiler Kit II (PPK2) between the mainboard and the battery. The PPK2 allows me to measure the CMOS current consumption during various modes of operation. Please ignore the dust 😉.
Powered off without AC
First I disconnected AC (the 230V power plug) and connected the battery.
That’s an average of 9.49uA. While that doesn’t sound much, many CR2032
batteries seem to have a capacity of 220mAh. Using the formula
220 mAh / 0.00949 mA / 24 h / 365 d we arrive at an estimated battery life of
roughly 2 years and 171 days. If we assume, that my mainboard was in storage
for a couple months before it was shipped to me, this matches my experience
pretty well.
Powered off with AC
As soon as I connect AC, without actually powering on the computer, the current consumption drops to 4.63uA. So if we’d keep AC connected all the time, we can expect a battery life of rougly 5 years and 154 days.
I can only assume, that this reduced power consumption is an unintended side effect of Gigabytes hardware design, because if they intended to extend the life of the CMOS battery while connected to AC, I’d expect to see 0uA.
Powered on
Next, I measured the current while the computer was powered on and showing the boot selection menu.
Interestingly, with 5.19 uA is a bit higher than while powered off, but still nowhere near the value I got with AC disconnected. With this, you can expect a battery life of 4 years and 306 days.
Powered off with ErP and no AC
Next I enabled ErP in the firmware settings. This setting is intended to reduce AC power consumption while the device is powered off, but still connected to AC. After turning off the system, I got the following result:
That’s 4.51uA or 5 years and 207 days. That’s expected because, ErP is supposed to save AC power, not CMOS power. I did not see any difference in the CMOS current consumption while powered on either.
Conclusion
If you want the reduce the number of times you have to take out your GPU to access and replace the CMOS battery, you probably want to keep your computer connected to AC. As for me, I don’t want to do that. Every device I don’t use gets disconnected completely - either using a smart plug or using a switchable power strip.
In my opinion, even 5 years of CMOS battery life is abysmal and Gigabyte should have never released a product like that. Some of my Nintendo NES cardridges also contain CR2032 batteries, which still work after 40 years.