The BIOS battery in a PC is a small, flat battery found on the motherboard. These batteries are most commonly lithium batteries and typically carry a 3-volt charge. They are responsible for keeping a stable current in the motherboard when the PC is powered off. These batteries have a limited life, and as they begin to wear out, you may experience difficulty with your system. The most common symptom is failure to maintain date and time. If you are concerned about the status of your BIOS battery, it can be tested using a multimeter, which can be purchased online or at a hardware or electronics store.
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Things you need
- Multimeter (digital or analogue)
- Small flathead screwdriver (optional)
Record any custom hardware settings. Do this by booting your PC and pressing either delete or F10 when prompted to load BIOS.
Unplug all power and accessory cables from your PC.
Remove the hard drive case from the PC chassis, and move aside or remove any cables or wires that block your view of the motherboard.
Identify your BIOS battery. It will be a disc, roughly the size of a quarter, held in place with a small spring clip. Push the spring clip gently against the battery housing to release the battery. You can use a small flathead screwdriver to help depress the spring clip if needed.
Place the BIOS battery, positive terminal down, on a flat, nonconductive surface, like wood or some other non-metallic surface such as a wooden desktop or cutting board.
Switch your multimeter on and set it to measure DCV. It will be marked by either
"DC" or by a single line above three smaller dashes.
Set your multimeter to measure at least 3 volts. Voltage may be abbreviated "V" on the multimeter.
Place the red, or positive, probe of your multimeter against the side of the BIOS battery and place the black, or negative, probe of your multimeter on the top face of the BIOS battery.
Record the measurement displayed on your multimeter. If the BIOS battery is brand new, it should read 3 volts DC. If the BIOS battery is weakening, it will read around 2.5 volts DC. If the battery reads below 2 volts, you will need to purchase a new battery.
Place the new (or functional old) battery back in the housing with the positive terminal facing up.
Reposition any cables or wires within the chassis that you may have moved or unplugged during step 3, and replace the chassis cover gently. Do not force the chassis cover. If it does not fit easily, you likely have a cable out of place.
Plug your PC back in, boot it up and enter BIOS as described in Step 1. If given the option, select "Load default BIOS settings." Once this is complete, you may restore any custom hardware settings that you recorded in Step 1. Save any changes and exit BIOS to boot to your operating system.
Tips and warnings
- BIOS batteries are common 3-volt lithium batteries. They can be purchased at general retailers, photography stores and electronics hobby shops.
- Discharge static electricity prior to doing any work with the motherboard by touching the metal side of the chassis while wearing an antistatic wristband or by some other means. Use of a grounding antistatic wristband is highly recommended; however, it is not necessary.
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