Doogee S60 - Can't hide/change battery icon
The answer lies in build.prop!

All credit for this goes to Nephiel on XDA-Developers (this post, specifically).

The Doogee S60 has the setting battery_view_land_show, which is defaulted to yes.
On a rooted phone, this setting can be changed easily using BuildProp Editor.
Set the value to no, reboot the phone, et voila! Back to the standard battery icon, and all expected behavior from GravityBox and such!