OK. Remember and look again at the main electrical system schematic from your course, or in the Part B.
You do need to clarify that LOGIC in a BOEING is nothing to do with computers but simply relay switching and suchlike. The NG is basically a digitally redrawn and simplified 737 airframe with mostly the same crap stuffed in it from before or modernised versions of the same crap. Essentially it's a simple old beast with a few cleaver boxes driving the screens.....
So, is the Battery is attached to the DC Bus? Is it driving the DC bus or are the TRUs driving it? Where is the current flowing from or to? The Battery is removable from the bus so is connected via relays. To know the voltage of the battery, you must sense the voltage from the battery side of this switched relay.
TRU output? Battery charger output? Remember a Battery is effectively a NiCad 24v device. to keep it tip top it is fed a slightly higher voltage to keep it fully charged.
Your car alternator feeds 14V to your 12v car battery. Measuring with a Volt meter when it's running will show 13.5-14.5v usually. Notice how you have to change the settings to see the load? DC load needs to go through the meter whereas voltage can be measured in parallel.
Remember, the 737 is not rocket science, just a loose collection of many different systems often designed in different decades flying in loose formation most of the time.
Good luck!