T&T: DC Voltage Measuring

[captiva at att.net]

Hi Group!

I've found different places that tell me what voltages of the house bank
represent a fully charged battery or one that is 50% charged, etc.  Since I
don't yet have a panel mounted dc voltage device, I've been using my multi
meter that is connected temporarily to a cabin lighting source to measure the
house bank voltage.  First, is what I'm reading a good indicator of battery
charge if nothing has been turned on for six hours or more?  After a night at
anchor with an anchor light on, is that voltage a good indication of battery
charge in the morning?  I'm trying to determine why (other than ease of use)
one would spend $150-$250 to see exactly what I'm seeing on my  multi meter.
Since I always turn off the starting batteries except when actually
starting/running, I don't see a reason to see their voltages on regular basis.
Am I missing something?  I've also seen a lot of references to shunts.  Does
my multi meter have one that takes the place of permanent shunts for an
installed dc voltage monitoring system?

Lots of dc questions here, so if anyone can direct me to one place to learn
more about battery monitioring, I'd be appreciative!  Guess you can tell from
the slant of the question that I have to be a previous sailer  :)

In advance, thanks for the info that I know I'll get from this great group.

Don Coleman
M/V Mi Boudreaux
Bristol Offshore 42
Lake Guntersville, Alabama