I'm pretty sure it can't be done. The battery icons you see are part of the icon Pack that RTI bought, but some can't be used the way you would think (and the way they should). Another one is the wifi signal meter icons. You can't use them to illustrate wifi.

What you could do is assign a button to the control panel screen, and look at the battery there, but if I recall correctly, I don't think it tells you battery charge status, only at what level to display the warning.

It would be great if there was a way to see battery level, but more importantly zigbee signal and connection.