I like to have the remaining battery indicator show in my task bar but after upgrading to Windows 10 I could only see it in the system trays secondary menu. To put it back onto your task bar; Right-Click the task bar->Properties->Notification Area: Customize ->Turn System Icons On/Off
In my case the battery icon was already on. Toggle it off and then back on again. Voila, battery indicator is back on the task bar.