Is there a way to tell about the auxilliary battery condition in a VW (or
any rig, for that matter)?  I've been working with all kinds of batteries
over the years and I always have been puzzled about how to find out what I
might expect from the battery.  I have a digital multimeter and I get
voltage readings but I'm told that is no real indicator of how good the
battery is charged or is capabale of being charged...
  Is there an instrument that I could wire into my systems (I have a few
different vehicles with multiple battery systems) where I might get an
actual meaningful readout that would tell me..."Hey, don't expect much more
from this battery till you charge it more" or "this battery is shot" or "all
your batteries are in fine shape with 100% charge"?
  I have seen battery condition indicator gauges in yachts..I've seen
voltage indicators on some rigs.  My travel trailer has an LED readout and
for that matter, so does my semi-westie van...but those things seem pretty
much a joke...
   What should I wire into my systems to give me a better handle on how much
juice I have in the batteries?  Is there anything that works..or do I just
have to keep guesstimating as I have been doing all these years?
  Thanks, Don Hanson