If you are plugged in, all lights on mean something like nominal 12-13 VDC is present in the system. If not all the lights are on and plugged in, you have a situation.
If you are not plugged in, All lights on mean you have something like a full charge on the battery or your solar system (if connected) is charging at above 12 or so volts. If not all the lights are on, you probably have a battery that is doing it's job and supplying power to the RV. If only two lights are on, you don't have much juice left. If only one light is on, you should have charged your battery already.
Voltage-based systems like this do very little to tell you what is actually going one, but they do say if you have juice, if your converter is operating or if you don't have juice. If you need more or better information, you need better instrumentation.
SF Bay Area '99 Ford E350 V10 '16 Rockwood 8329SS
X2. If you are plugged in and all lights are lit...your converter is charging your batteries. If you are not plugged in and your engine is running (TV or motorhome) all lights are lit means that your alternator is charging the house batteries. If you have solar and all lights are lit it means that your solar system and charge controller are working. In any of those circumstances, if all lights are not lit, it means you have a problem with your alternator, BCC, converter or solar solution (as long as the sun is out!)
With nothing running or plugged in, the lights will give you a guess as to battery state of charge. If you have been charging that guess will be high. I you have been discharging...that guess will be low.
Forget the lights....in the first place...voltmeter reading with a battery connected are meaningless. So even if you had a digital readout...they are meaningless.
All you can glean from the lights is that....the battery is depleted OR the converter is on.
Just to add in on the confusion about the idiot lights they put on the panel. The posters above are correct, they tell you if you are charging, or discharged, with not much in between, and with no loads. These lights will tell you a little bit about your state of charge, but not much. When you charge your battery bank, the voltage will remain higher when you first disconnect your charger. The batteries will hold a higher voltage reading for 12-36 hours, and show a higher readout- despite what the real state of the battery is in. So, knowing that, you can sort-of use that as a guideline. When towing, you will get very little charging to your batteries due to many reasons covered elsewhere in the forum, despite what your lights tell you.
1987 Starcraft Nova tent trailer, purch. '87, sold 8.14
2013 Crusader 290RLT bought new, 8.14
2001 Ford F-250 7.3
A Loving wife and Mason the always dirty dog!
Herk provided the OPs answer. and everyone else is correct with that said the lights are good for a quick check without dragging out a volt meter or disconnecting batteries. plugged in hit the button all light on converter working, unplugged hit the button to see if its time to start your gen and recharge.
Jake my sidekick (yellow Lab)
2006 F350 6.0
2016 Flagstaff 26 FKWS
AF&AM of Idaho