Reminds me of a somewhat unrelated scenario in Android world. Auto backup of photos in Google+ Photos has a setting where you can have backup only happen when connected to power (and/or on Wi-Fi). Perhaps Microsoft could add something like this in their settings as well?

Yes, I understand this could be seen as feature creep but I think if the savings in battery life are as much as the grandfather says then it is worth the extra complication of a setting. What do you think?