BIOS stands for Basic Input Output System and is the laptop’s actual firmware. The software stored in the BIOS is activated immediately after you turn on the computer. The BIOS then ensures, for example, that the operating system is loaded and started.
The standard battery type is a CR2032 or CR2025 lithium coin cell with a lifespan of 5 to 10 years.
If your BIOS settings get messed up or a reset is needed, temporarily removing the BIOS battery or the main battery often helps. This article covers battery types, the procedure, BitLocker risks, and what should be checked after a repair.
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Signs of a dead BIOS battery
- Incorrect system time after every startup
- Error message “CMOS Checksum Error” during boot
- Loss of BIOS settings (boot order, fan profiles)
To ensure that saved data is retained even if the power supply is interrupted, (almost) every laptop has a small battery that stores the BIOS settings: the laptop BIOS battery.
In some cases, it can be helpful to reset the BIOS to factory settings—for example, if you made incorrect settings in the BIOS and the system no longer works properly as a result. Depending on the laptop manufacturer and model, there are different methods for performing a BIOS reset via the operating system.
However, the safest method is to briefly remove the BIOS battery. We’ve put together everything you need to keep in mind in this article.
Locating the laptop BIOS battery
First, you need to open the laptop and locate the BIOS battery. Very often, the laptop BIOS battery is a standard CR 2032 battery, which is either mounted directly on the motherboard in a socket or connected to the motherboard via cables and a connector.
However, many current laptop models no longer have a dedicated laptop BIOS battery at all. In that case, the built-in laptop battery is used to supply the BIOS chip with power continuously.
Performing a BIOS/UEFI reset correctly
To perform a BIOS/UEFI reset, you need to briefly remove and reinstall the laptop BIOS battery—or, if there is no separate BIOS battery, the laptop battery.
How long the battery needs to be disconnected to guarantee a BIOS reset depends on whether there is still short-term buffering via capacitors, for example.
Usually it’s only a few seconds, but a few minutes should definitely be enough to ensure the correct BIOS reset. Another option is to briefly short the two contacts on the motherboard after removing the BIOS battery.
A curiosity when removing a laptop BIOS battery on a DELL laptop
While researching this topic in our notebook workshop, one of our technicians reported a curious case. During a laptop repair, the laptop BIOS battery was briefly removed on a DELL laptop. When the repair was finished and the laptop was started again, the system unexpectedly asked for the BitLocker key.
BitLocker is a Microsoft encryption product that protects user data on the computer. If a BitLocker issue occurs, you’ll see a prompt for a BitLocker recovery key. If you don’t have a working recovery key, you can’t access the computer. You need this key, for example, if you want to install a hard drive in another device, the RAM changes, or a different motherboard is installed. Up to that point, we had never experienced a BIOS reset triggering a BitLocker key prompt.
So we were in a tough spot. Our customer couldn’t provide a recovery key. So we had to look for another solution. After some research, we managed to disable a security feature on this DELL laptop so that this prompt for the BitLocker key no longer appeared.
Note on repairs for notebooks with built-in batteries and no dedicated BIOS battery
As a general safety measure, a notebook should be powered down before any repair by removing the battery. On devices with a built-in battery and no dedicated BIOS battery, however, this inevitably leads to the loss of BIOS settings.
In these cases, after the repair you usually need to set the date and time again in the BIOS, and in rare cases more as well—for example, switching UEFI/Legacy mode.
No BIOS battery installed in the notebook
Many current laptop models no longer have a dedicated laptop BIOS battery. In that case, the built-in laptop battery is used to supply the BIOS chip with power continuously.
Where can I order the CMOS battery?
You can buy over 17,000 CMOS batteries in our shop.
Our IPC computer technicians carry out hundreds of BIOS and motherboard repairs every year—so we’re familiar with rare cases too, such as BitLocker key prompts after BIOS resets. BIOS repairs are almost always worth it.