Battery Level

I have a monitoring systems that monitors the battery, fresh, black and gray water in a single monitor.  I assume this is standard to all rpods.  There are four levels: Full, 2/3, 1/3, and Empty. My question is how accurate is this unit for monitoring battery level?  If it is accurate at what level should I consider charging my flooded batteries before I run then too low and hurt them.   

I know how to read the battery voltage via a voltmeter.  Is that what you are talking about? I'm trying to determine when I'm about 50% down and I need to charge the batteries so I don't hurt the batteries by taking the charge down to far.    I'm planning on doing some boondocking and I don't want to ruin my battery if I can help it.  

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+1 to Marwaynes post.  A voltmeter is a cheap but necessary tool you need to keep an eye on your battery strength.  I purchased mine years ago at Harbor Freight for $3.  The two batteries I own are 12v Interstate group size 24 deep cycles.  Purchase dates are 12/2010 and 3/2011.  They were last charged October 31 and Nov. 1 on a 2 amp trickle charge for 24 hours each and currently reside on a cement floor in an unheated garage.  A few days ago the voltage was read and recorded.  12.59v and 12.71v; not bad for batteries of this age.

Look into getting two 6V deep cycle golf cart batteries and connecting them in series. Case size GC2. They are the largest size that will fit on the tongue, have the most available capacity, are designed to handle deep cycling, and are very cost effective. Also, the series connection is better than two 12V batteries in parallel because it keeps the same current flowing in and out of both batteries. The drawback is tongue weight, which will go up by 70-80 lbs so be sure your tow vehicle can handle it.