In general, it's considered bad practice to have a meter draw power from what it is measuring. However in this case the power requirements of the meter are so small compared to the capability of the battery
that it shouldn't be a problem. That said, the meter should be treated like any other parasitic load. Just like hardwired LP and CO detectors, over time it will discharge a battery. I'm guessing it requires 10-20 mA.
P.S. glad to see Marlin P Jones is still around. Most of the hobby parts suppliers are long gone.