Percentage Battery Proxmox:
cat /sys/class/power_supply/BAT0/capacity
cat /sys/class/power_supply/BAT0/status

Percentage Battery Windows Powershell:
Get-CimInstance -ClassName Win32_Battery | Select-Object BatteryStatus, EstimatedChargeRemaining, DesignCapacity, FullChargeCapacity

Get-CimInstance -ClassName Win32_Battery | Select-Object Status, BatteryStatus, EstimatedChargeRemaining | Format-List