This is an adequate HF load testing unit for testing strength of "starter" batteries.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90636

Also useful for spot checking your camping battery.
I got mine on sale for between $15-$20 if I remember correctly.

Testing your start battery with a voltmeter at rest without a load doesn't tell you too much...a "dead" battery could still read close to 12V.

You should at least measure voltage when cranking or headlights and blowers on etc ...

---------- Original Message ----------------------------------
From:         Alan Felder <dieseldoofus@GMAIL.COM>
Reply-To:     Alan Felder <dieseldoofus@GMAIL.COM>
Date:          Tue, 26 Jan 2010 18:53:15 -0600

>Here is a device that will test your battery:
>
>*http://tinyurl.com/352k4l*
>**
>It's not portable, but you should use a load around half your battery's CCA
>rating, and since I have a diesel and 800 AmpsI needed this larger one.  You
>may get by with a smaller one which HF also has a variety of.  It puts your
>battery under a known load (inside the box) and following directions, will
>let you know what shape your battery is in, in static mode that is.
>
>Alan Felder
>
>
>On Tue, Jan 26, 2010 at 1:49 PM, Don Hanson <dhanson928@gmail.com> wrote:
>
>>  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
>>
>
>
>
>--
>Alan Felder
>Austin TX
>82 Diesel Westy
>