With the picker on top of the screen you can select the battery. By definition the main battery always is number 0. The backup battery - if there is one - has the number 1.
For some categories the value is "Unknown". By definition this meens, the battery manager in the Newton device dosn't provide this information. Although a categorie shows a value one time, it's possible in the next moment it shows "Unknown". The author was be able to observe this on a MP 130 in the categorie AC Power applied. This behavior is not a bug in SBM Utilities, it's by design of the Newton system.