The battery-charging tag is redundant, and I propose that it should be merged into batteries.
The process of charging and discharging is intrinsic to the concept of a battery, so I suggest that charging/discharging questions don't need another tag for further disambiguation. The lack of a battery-discharging tag is further evidence that we don't need the battery-charging tag.
And battery-charging has no tag wiki or excerpt written about it.
There are 17 questions currently tagged with battery-charging tag. Of those, 70% already have batteries. All of the remaining questions are clearly also about batteries.