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February 26th, 2026 21:56

XPS 13 9305, Bios battery drains to fast, doesn’t turn on

I have a Dell XPS 13 9305, and I’ve had to replace the BIOS battery (ML1220) twice within one year. When the BIOS battery is empty or not connected, the laptop will not turn on, even when it is connected to the AC adapter.

I measured the voltage while the laptop was on, and the charging voltage was between 2.5–2.7 V. When the laptop is turned off but both the main battery and AC adapter are connected, the BIOS battery is not charging and instead drains quite quickly.

Can anyone help me determine whether this is a known issue or what I can do about it? I cannot turn on the laptop when the BIOS battery is low, and I have to replace it twice a year.

DELL-Daniel V

Community Manager

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223 Posts

February 26th, 2026 22:35

Contact Dell GHN (Get Help Now) chat technical support Monday through Friday. Click the blue "Get Help Now" on the right to start a private live chat session. Share the private Service Tag with them so that they can verify the ownership and warranty status. This will also generate a unique Technical Support case for your unique Service Tag. If already out of warranty, click here for the Dell out of warranty offerings.

There are no known issues that I can see about the CMOS draining in this manner. If you constantly need to replace the CMOS battery, then you may want to look into replacing the motherboard assuming the standard battery is in good condition. 

Battery Storage Mode and how it Affects the CMOS Battery Shelf Life

This article may not entirely apply if you're using the system on the daily, but it does give some insight as to why a CMOS battery may drain. After the battery is in Storage mode, the CMOS battery is used to keep the time and Custom BIOS settings. The CMOS battery lasts for approximately sixty days if fully charged. After this time, the Bios will lose its Custom settings. I'd actually recommend running the preboot diagnostic to ensure its passing. You can also view the battery health within the Advanced test page. 

  1. Shutdown the unit
  2. Hold down the Fn key and the power button together
  3. The quick test should automatically start
  4. Should the quick test pass, then click on Advanced Test
  5. Click on System Info on the left hand side
  6. The system battery Health will be listed here. If Excellent or Good, then the system battery should be fine

If there are no errors for the battery and its in good health, then the CMOS draining shouldn't be attributed to the battery and should instead be attributed to the system board not maintaining the charge cycle/voltage. I would just ensure the system BIOS is at the latest available version on our support site so that firmware isn't attributed to the drain here. Even if the battery was degraded to a fair or poor health, I can't say I've seen it cause the CMOS to fail like this. I'd lean on the board to be the issue, but if out of warranty, then it may be more cost effective to try replacing the system battery first. 

(edited)

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