You cannot directly read the battery voltage when it is connected to the converter. You can read the state of the converter voltage, and that depends on the type of battery and the current mode of the converter/charger. Assuming lead acid batteries (not AGM):
Absorption mode: 13.6VDC
Bulk mode: 14.4VDC
Float mode: 13.2VDC
When you are using the DC appliances in the coach, your charger will probably be in Absorption mode as it is replacing demand from the battery/or being supplied by the charger. This mode not only provides slow charge to the battery, it is the primary power-supply mode of the converter.
99% of the time in operation, your system will be (or should be) in this mode.
When you are not actively drawing any current from the coach, and the batteries are fully charged, the charger should switch into Float (trickle) mode, which keeps a top-off, or trickle charge on the battery.
In practical experience though, you may never see this mode as all of the low-level loads (fridge, water heater, furnace control boards, TV amplifier, contactor, etc) might keep enough load on the battery that it is always in discharge mode.
Bulk charge is the primary fast-charge mode, used when the battery needs significant recharge. It is limited to 4 hours in the WCFO chargers.
Bulk mode = fast charge.
Absorption mode = slow charge.
Float mode = top off charge.
Each of these charge modes apply a different voltage to the system.
Some chargers also have a Desulfation mode, which basically cycles the Bulk mode on for a few minutes every day to keep the batteries healthy... but I am not so sure this is really a huge advantage.
If you want to measure the battery itself, it has to be disconnected and at rest for 24 hours to get an accurate measurement - although a reasonably accurate measurement can be achieved with a 1 hour rest.
When disconnected, a Lead Acid battery should read:
100% charged = 12.6VDC
75% charged = 12.4VDC
50% charged = 12.2VDC
25% charged = 12.0VDC
0% charged = 10.8VDC
(AGM and Gell batteries will have slightly different voltages).
Note also that on Thor coaches, disconnected can only be assumed if the battery cables are disconnected, as even if disconnected by the disconnect switch - some parasitic loads may still be present.
Hey Jamie; here is another project we need to do - build a window comparator to show the charge mode...
Maybe it's a function I can add to my yet unrealized tank monitor project.
The only thing that works on a RV is the owner...