Detect when the system is running off of battery power, and allow the user able to configure whether or not seeding and/or downloading should be allowed while on battery.
I don't know what load is typically needed before qBittorrent starts using up significant energy, but I imagine it could still help conserve energy while on battery (or give a server more runtime if running on UPS).
I have not done any programming related to battery events, so I might not be able to implement this myself anytime soon. I understand implementing such a feature may vary considerably between platforms.