hi.
To your first (implied) question: I don’t know if the battery problem could be related to the update. but since there have been many complaints about the updated and it has been rivesed for them it’s surely a possibillity.
Darker backgrounds use up less battery than light ones and still pictures use less than live wallpapers. but a 5:1 loss in battery runtime is probably more than that.
I don’t know of a “set to standard” option, is that a new thing with the 1.8 update or are you using a different launcher?
Usually you have to go to settings > Display > Wallpaper > Wallpapers > and “Set Wallpaper” to get the default wallpaper back.
Did you install any apps lately that might drain your battery? Or changed settings, like brightness or bluetooth/gps/wifi switched on?