As keelhauler mentioned, a simple volt meter provides something. Though it can be misleading, it is better than nothing.
I installed a voltmeter in our stove hood.
CLICK HERE for pictures of the volt meter and installation, applicable to PCs with the older stove hood design. Because it is in plain sight, I learned how to interpret the reading. It basically comes down to what is turned on at the time you look at the voltage. The voltage drops with more stuff running. It does help me understand what things turned on, are hard on my batteries.
Though the volt meter is not ideal, I still find it very useful, so much better than relying on the PC-supplied LED lights on the inverter and stove hood read-out. By the time both read-outs said it is time to charge the batteries, I waited way too long. I made a decal of how to interpret the voltage reading and stuck it on the inside of the cabinet door above the sink.

We boon dock almost exclusively and we have a tow vehicle which keeps our PC parked. I learned it is best to run the generator every morning for about an hour, and sometimes a little more when we return from a day out. I prefer using a secondary battery charger instead of the on-board Tripp-Lite because it charges faster and tells me how it's going.
Here is how I utilize my charging time more effectively. The readout is "charging amperage" which never gets to say "FULL" when camping because something in the rig is always running. I really need to update this picture now that I have two 6V batteries without a battery tray.
