I tried to reduce suspend battery drain on my Dell Latitude 5501 running Ubuntu 24.04.

The default suspend mode was s2idle, and the suspend power draw looked too high: around 10W. Since the machine also exposed deep sleep, I tested ACPI S3 to see whether it could save more power.

Short version:

deep sleep saved power in theory, but resume was not reliable enough.

Even after updating BIOS and testing a newer kernel, the machine could still freeze after resume. I went back to s2idle.

• 1. Machine
• 2. Enabling deep sleep for one session
• 3. What the logs showed
• 4. BIOS update did not fix it
• 5. Newer kernel looked better, then still failed
• 6. Conclusion
• 7. Useful commands
• 8. Takeaway

1. Machine

The test machine:

Model: Dell Latitude 5501
BIOS before: 1.25.0
BIOS after: 1.44.0
GPU: Intel UHD 630 + NVIDIA MX150
Original kernel: 6.8.0-41-generic
Later test kernel: 6.8.0-134-generic
NVIDIA driver: 580.159.03

The default sleep mode was:

cat /sys/power/mem_sleep

Output:

[s2idle] deep

So Linux was using s2idle by default, but deep was available.

2. Enabling deep sleep for one session

I first enabled deep only for the current boot:

echo deep | sudo tee /sys/power/mem_sleep

This is a good way to test before making the setting persistent. If it breaks, a reboot should return the machine to the default mode.

After suspending and resuming, the laptop froze. I had to hard reset it.

3. What the logs showed

The logs confirmed that the system entered deep sleep:

kernel: PM: suspend entry (deep)

But I did not see the normal resume lines that I would expect after a successful wake:

ACPI: PM: Waking up from system sleep state S3
PM: suspend exit
nvidia-resume.service

That made the failure look quite low-level.

My reading is that the machine did not get far enough back into Linux for the kernel and services to log a normal resume path. It looked more like a firmware, kernel, or device-resume failure than a regular userspace crash.

4. BIOS update did not fix it

The machine was originally on BIOS 1.25.0.

I updated it to BIOS 1.44.0, then tested deep again.

The result was still bad:

deep sleep still froze after resume

So at least on this machine, the BIOS update alone was not enough to make ACPI S3 reliable.

5. Newer kernel looked better, then still failed

Next I installed a newer Ubuntu kernel:

6.8.0-134-generic

I also checked that the NVIDIA DKMS module was built for it:

nvidia/580.159.03, 6.8.0-134-generic, x86_64: installed

This looked promising at first.

With BIOS 1.44.0 and kernel 6.8.0-134-generic, the laptop appeared to resume successfully from deep. It stayed alive for about a minute after wake.

Then it died or froze again.

That made the result worse than a simple pass or fail. The resume path was improved enough to come back briefly, but not stable enough to trust.

6. Conclusion

My conclusion for this machine is:

On my Dell Latitude 5501, deep/S3 sleep is still not reliable on Linux,
even after BIOS 1.44.0 and kernel 6.8.0-134.

I gave up and went back to s2idle.

The suspend power consumption is worse, but stability matters more. Saving battery is not useful if resume can randomly kill the session.

7. Useful commands

Check the available and active sleep mode:

cat /sys/power/mem_sleep

List previous boots:

journalctl --list-boots --no-pager

Inspect the previous boot:

journalctl -b -1 --no-pager -n 250

Filter kernel logs for suspend, resume, ACPI, NVIDIA, and likely failure clues:

journalctl -b -1 -k --no-pager | grep -Ei 'PM:|ACPI: PM|suspend|resume|waking|deep|nvidia|i915|i2c|watchdog|lockup|panic|BUG'

Check DKMS status:

dkms status

Check the running kernel:

uname -r

8. Takeaway

If your laptop drains too much battery in s2idle, deep can look tempting.

But on hybrid Intel/NVIDIA laptops, ACPI S3 can still be a trap. Test it carefully before making it persistent.

For this Dell Latitude 5501, I am staying with s2idle for now.