Lazy Daze Owners' Group

The "idiot light" battery condition display on the panel uses a simple circuit to light the three LEDs depending upon the battery voltage. There are several problems with this. The circuit isn't exactly well-calibrated. Even if it were, a three-stage display is too coarse to tell you much. And even if the display were an accurate digital voltmeter, it wouldn't be a good indicator of the batteries' state of charge (SOC), because in normal use there are always drains and charging sources (solar panels, etc.) influencing the voltage.

If you wait until, say, three in the morning, when there's been no charging or appliance usage for many hours, and then read the battery voltage (without turning on any lights, mind!) using a digital voltmeter, you can get a reasonable idea of what the batteries' SOC is. Otherwise, voltage measurements don't really tell you much. In short, the idiot lights are next to worthless.

As Joan said, an "amp counter" type battery meter such as the LinkLite or Victron BMV700 can be useful, although these meters are heavily dependent upon knowing your battery bank's capacity and need recalibrating every year or so as that capacity diminishes with age. Better still is a Balmar Smartgauge, which calibrates itself continuously. I have both, but I trust the Smartgauge over the BMV700 for knowing what shape my batteries are in. (Amp counter meters such as the BMV700 do have other uses, such as knowing exactly how many amps are going into or coming out of your batteries at any given moment.)

Why didn't Lazy Daze install a Smartgauge? Well, the LED idiot lights and associated circuit probably cost a couple of bucks, while a Smartgauge costs a couple hundred. It's well worth it, though, if you do much dry camping!