The only way to have something show up in the system tray (the notification area) is to open the program that runs it. sometimes It is hard to find were the program is but that is the only way.
Trying to bring it up with customize notifications will not work (as you well know).
Try rebooting your computer. This will run all of the processes that run on startup. It might come up. This might run the program automatically
If this doesn't work or you want to be able to bring it up if it disappears again you need to use the taskmanager. Are you familiar with the taskmanager? Let me know. you can open it by holding down CTRL + Shift + Escape. On the process tab see if you can find a process that sounds remotely like a battery something or other.
Do a google search for the process i.e. process.exe. See if it looks like what you are talking about. Usually one of these websites will say where this program is located.
look on your computer too see if you can find the program that runs your battery display. If you open up the program when the battery indicator is gone, this should bring it back.