Your system information
- Device: Lenovo Legion Go S 8APU1 (Model 83N6), AMD Ryzen Z1 Extreme
- SteamOS version: 3.8.25 (BUILD_ID 20260807.2)
- Opted into SteamOS beta?: Yes
- Kernel:
6.18.42-valve2-1-neptune-618 (built 2026-08-08 03:48 UTC) — regression appeared right after this kernel replaced the previous 6.16.12-drmexec7-valve24.5-1-neptune-616
- Have you checked for updates in Settings > System?: Yes, fully up to date
Please describe your issue in as much detail as possible
After updating to SteamOS 3.8.25 (which bumped the kernel from 6.16.12-drmexec7-valve24.5 to 6.18.42-valve2-1-neptune-618), a yellow exclamation mark now appears next to the battery indicator in Game Mode.
journalctl -k shows the kernel spamming this line continuously, roughly once per second:
ACPI: \_SB_.BAT0: _BCT evaluation failed: AE_NOT_FOUND
Over one ~4.5 hour session this produced 16562 occurrences.
I compared two consecutive boots on the exact same hardware/firmware:
- Boot with the old kernel (
6.16.12-drmexec7-valve24.5-1-neptune-616, before the update): 0 occurrences of this error.
- Boot with the new kernel (
6.18.42-valve2-1-neptune-618, right after the update installed): error starts immediately and repeats continuously for the rest of the session.
_BCT is the ACPI "Battery Charging Time" method. The Legion Go S EC/DSDT apparently doesn't implement it (AE_NOT_FOUND), which by itself may not be new — but the new kernel appears to poll it far more aggressively (about once a second, indefinitely) instead of failing silently/once, and this seems to be what's surfacing the warning icon in the Game Mode battery UI.
Battery health/charge itself looks fine — upower and /sys/class/power_supply/BAT0/uevent both report correct values (99%, status Full, warning-level: none), so this looks like a UI/kernel-polling regression, not an actual battery problem.
I searched existing issues and didn't find a duplicate — closest related reports are #2458 (different device, different SteamOS version, different mechanism — battery draining under load despite charger connected) and #2674 (same device family but Z2 Go variant, charge-limit-overshoot symptom, pre-dates this kernel).
Steps for reproducing this issue
- Update to SteamOS 3.8.25 (BUILD 20260807.2) / kernel
6.18.42-valve2-1-neptune-618 on a Legion Go S.
- Boot into Game Mode.
- Observe the yellow exclamation mark next to the battery indicator.
- Confirm via
journalctl -k | grep _BCT — continuous _BCT evaluation failed: AE_NOT_FOUND spam, roughly once per second.
Expected behavior
Battery indicator shows the normal icon; _BCT (or its absence) should be handled gracefully by the kernel without indefinite polling/error spam, same as on the previous kernel.
Actual behavior
Battery indicator shows a warning (yellow exclamation mark) in Game Mode. Kernel log is flooded with ACPI: \_SB_.BAT0: _BCT evaluation failed: AE_NOT_FOUND, roughly once per second, starting exactly at the kernel version bump and continuing indefinitely across the session. Actual battery charge/health data (via upower/sysfs) remains correct.
Your system information
6.18.42-valve2-1-neptune-618(built 2026-08-08 03:48 UTC) — regression appeared right after this kernel replaced the previous6.16.12-drmexec7-valve24.5-1-neptune-616Please describe your issue in as much detail as possible
After updating to SteamOS 3.8.25 (which bumped the kernel from
6.16.12-drmexec7-valve24.5to6.18.42-valve2-1-neptune-618), a yellow exclamation mark now appears next to the battery indicator in Game Mode.journalctl -kshows the kernel spamming this line continuously, roughly once per second:Over one ~4.5 hour session this produced 16562 occurrences.
I compared two consecutive boots on the exact same hardware/firmware:
6.16.12-drmexec7-valve24.5-1-neptune-616, before the update): 0 occurrences of this error.6.18.42-valve2-1-neptune-618, right after the update installed): error starts immediately and repeats continuously for the rest of the session._BCTis the ACPI "Battery Charging Time" method. The Legion Go S EC/DSDT apparently doesn't implement it (AE_NOT_FOUND), which by itself may not be new — but the new kernel appears to poll it far more aggressively (about once a second, indefinitely) instead of failing silently/once, and this seems to be what's surfacing the warning icon in the Game Mode battery UI.Battery health/charge itself looks fine —
upowerand/sys/class/power_supply/BAT0/ueventboth report correct values (99%, statusFull,warning-level: none), so this looks like a UI/kernel-polling regression, not an actual battery problem.I searched existing issues and didn't find a duplicate — closest related reports are #2458 (different device, different SteamOS version, different mechanism — battery draining under load despite charger connected) and #2674 (same device family but Z2 Go variant, charge-limit-overshoot symptom, pre-dates this kernel).
Steps for reproducing this issue
6.18.42-valve2-1-neptune-618on a Legion Go S.journalctl -k | grep _BCT— continuous_BCT evaluation failed: AE_NOT_FOUNDspam, roughly once per second.Expected behavior
Battery indicator shows the normal icon;
_BCT(or its absence) should be handled gracefully by the kernel without indefinite polling/error spam, same as on the previous kernel.Actual behavior
Battery indicator shows a warning (yellow exclamation mark) in Game Mode. Kernel log is flooded with
ACPI: \_SB_.BAT0: _BCT evaluation failed: AE_NOT_FOUND, roughly once per second, starting exactly at the kernel version bump and continuing indefinitely across the session. Actual battery charge/health data (via upower/sysfs) remains correct.