If you use your Dell XPS 9300 plugged into an external monitor or dock most of the day, keeping the battery constantly charged at 100% will degrade its lifespan over time. The standard Linux advice is to write a limit to /sys/class/power_supply/BAT0/charge_control_end_threshold.
However, if you’re on Fedora with a Dell XPS, you might notice the hardware completely ignores this kernel-level setting. Here is how to actually fix it by talking directly to the Dell BIOS.
The Problem
Dell laptops handle power management through their proprietary SMBIOS extensions rather than standard ACPI battery thresholds. Even if the system files report an 80% limit, the firmware will keep charging the battery to 100%.
The Solution: smbios-battery-ctl
To set a real hardware-level charge limit, we need to use Dell’s native SMBIOS utilities. They are available in the official Fedora repositories.
1. Install the Required Tools
You will need the base library and the Python utilities that provide the command-line interface. Open your terminal and run:
sudo dnf install libsmbios smbios-utils-python
2. Set the Custom Charge Interval
Dell uses “charging modes”. To stop the battery from charging to 100%, we need to switch the mode to custom and define a charging interval.
For a desk-bound setup, starting the charge at 75% and stopping at 80% is ideal. Run the following:
sudo smbios-battery-ctl --set-charging-mode custom
sudo smbios-battery-ctl --set-custom-charge-interval 75 80
Because this command writes directly to the BIOS NVRAM, this setting is fully persistent. It will survive reboots, OS updates, and even works while the laptop is powered off.
You can verify your current configuration at any time with:
sudo smbios-battery-ctl --get-charging-cfg
Bonus: Quick Bash Aliases
Manually typing these commands every time you need to travel and want a full battery is tedious. Add these aliases to your ~/.bashrc (or ~/.zshrc) to easily toggle between “Desk” and “Travel” modes:
# Dell XPS Battery Management
alias bat-desk='sudo smbios-battery-ctl --set-charging-mode custom && sudo smbios-battery-ctl --set-custom-charge-interval 75 80 && echo "🔋 Desk mode: 80% limit active"'
alias bat-travel='sudo smbios-battery-ctl --set-charging-mode standard && echo "⚡ Travel mode: 100% standard charge active"'
alias bat-status='sudo smbios-battery-ctl --get-charging-cfg'
Now, just run bat-desk to preserve your battery health while docked, and run bat-travel the night before a trip so you wake up to a 100% charge.