I recently noticed that the remaining battery time stopped showing on my laptop. I started digging into it and found these lines to be problematic:

https://github.com/tmux-plugins/tmux-battery/blob/master/scripts/battery_remain.sh#L118-L123

for whatever reason, my laptop natively running Linux snejugal 7.0.3 #1-NixOS SMP PREEMPT_DYNAMIC Thu Apr 30 09:13:05 UTC 2026 x86_64 GNU/Linux is detected as WSL by is_wsl (changed in #119). then the scripts starts looking for charge_full, charge_now, current_now in /sys/class/power-supply but can't find any. that's because these are actually (I guess) energy_full, energy_now and voltage_now on my machine:

$ ls /sys/class/power_supply/BAT0
alarm           charge_control_end_threshold  energy_full         extensions    model_name  present        subsystem   uevent
capacity        cycle_count                   energy_full_design  hwmon3        power       serial_number  technology  voltage_min_design
capacity_level  device                        energy_now          manufacturer  power_now   status         type        voltage_now

I guess this might have changed in recent Linux versions or depends on the driver.

print_battery_remain also supports upower and that works just fine, but my natively running Linux is detected as WSL, so that branch can never be reached. so I see a few problems here:

1. the code gated behind is_wsl supposedly became outdated;
2. this manual work with /sys interfaces is the primary way to calculate remaining time, not a fallback in case other tools are not available;
3. one can't choose the backend to use.