If that pref it is set to true the battery API will be enabled (usable). If you want to prevent the API from being used you set that to false. Setting it to false should break the battery fingerprinting tests. Note that you can open about:config and search for ".enabled" (without double quotes) to find other enable/disable prefs. I think most follow the .enabled convention but some don't. You'll find some .enable (without the d) ones for example. Most prefs are documented/discussed in numerous places, so if you want more info about one you can right click copy the pref name and "google it".
It's battery status now. What next? Having the ability to change about:config preferences is fine as a workaround but I am of the opinion it is not sustainable to expect anyone to keep up in checking if each and every web standard can be abused.
Firefox to prevent sites from tracking users by checking their battery status https://www.helpnetsecurity.com/2016/11/03/firefox-battery-status-tracking-users/
I have been trying the "Privacy Settings " extension in FF . Instead of having to wade through all that stuff in about:config , this gives a reduced set with on/off switches for each . The dom.battery setting is in the list . I enable it when needed ( like just now ) but keep it disabled otherwise .
i found this helpful for protecting several applications....dom.battery being one of them.. https://www.privacytools.io/