Frequent CMOS Battery Changes?

The Gigabyte GA-Z77X-UD5H motherboard in my desktop PC has started needing a new CMOS battery every 6 months. The PC fails to boot and stops with error code db. The open circuit CMOS battery voltage at this point is 2.8V. Both times I've fitted a new Duracell battery showing 3.0V+ and all has been fine. On resetting the BIOS details, I noted the date was wrong so the BIOS had lost its settings.

The PC is used about 3 hours a day but otherwise turned off at the mains. Is there a motherboard problem which would cause the CMOS battery to drain so quickly or perhaps I have a duff batch of batteries?

It could be the batteries, but unlikely. Do you have a voltage tester?

The first thing that occurs to me is that the MB is drawing power while off for some as yet unknown reason. Normally the battery just powers the Real Time Clock and the EEPROM that maintains the BIOS/UEFI. That draws very little power and a battery can last for years.
I would start by going through the BIOS/UEFI settings to see if there is anything set to stay on after a full off condition.
Otherwise it could be a fault on the motherboard.

Couple other thoughts:
Bad Ground: If the motherboard has a bad ground (short circuit to ground) or missing ground screw, that could do it.
Power Supply: the supply, when in the PC off but still plugged in and power supply switched on should feed the board through the 5VSB circuit. If that is defective, or on a modular supply loose, then the battery is doing all the work.
Can you try a different PS?

The battery is used when there is no power so if you turn off power the time it lasts is about. Right

I have Notebooks and couple of Desktops that go weeks at a time unplugged from commercial power and the RTC/CMOS/BIOS battery on them does not have to be changed for quite awhile. That small battery isn't recharged. I have seen a couple older Notebooks that had that function as part of the main battery and could be depleted but recharged when back on power. A motherboard could have a fault that is draining the battery.

The older AT-style computers had a power switch attached directly to the power supply but the newer ATX-style have the On/Off switch attached to the motherboard and pressing it tells the computer to wake up, the power is always On until unplugged from commercial power and the Notebook battery removed.

Samuria said:

The battery is used when there is no power so if you turn off power the time it lasts is about. Right

The PC is off at the mains for 21 out of 24 hours so the 5V standby supply is not powered up. I guess its possible I could have a batch of counterfeit Duracell batteries from Amazon which have a poor capacity.

The RTC/CMOS/BIOS battery is usually 3V, not 5V, and its not actually a standby use, only intended to maintain the computer's settings when turned off or unplugged. It's frequently a CR-2032 but some boards use different sizes. Some older Notebooks used a 'cartridge' made of smaller batteries soldered together and encapsulated, mostly to fit the board and cases.

Megahertz said:

Do you live near by the sea?
Do you see oxidation on the MB?

The MB looks like new