On Sat, May 8, 2010 at 5:37 AM, Michael Sullivan <sandwichhead@gmail.com>wrote:

> I am now at 12.08 on main and 12.20 on aux after van sat overnite.  I feel
> there is a drain somewhere.  Any tips on how to check this before I take it
> to a battery guy?
>

Other may suggest something else but here's what I'd do.
The symptoms you describe imply either low charging from the alternator or a
battery going bad.
First, check for current drain with the engine off, key out.  You should see
no more than 20-50 milliamps.  If much more than that then something is
draining current when parked.  You check this by disconnecting one of the
battery cables, preferably the ground, setting your multimeter to it's
highest amperage setting (usually 10 amps on most meters today) and
connecting the meter between the cable and the battery post.  If the reading
appears to be zero or very low you can change to a more sensitive setting.
Next, with the engine running, check the output of the alternator AT the
alternator.  You should see about 14.2-14.4 volts.  Now check the voltage at
the starting battery.  You should see about the same, maybe just little
lower. If you are seeing much less at the alternator the alternator is not
putting out what it should, possible problems would be worn brushes, bad
regulator, or the alternator going bad.
If you want to eliminate the aux battery/charging system from the equation
just disconnect the wire that goes from the starting battery to the 1315.
To check the battery itself give it a full charge with a good battery
charger.  Note the voltage about a half an hour after the charge is complete
and the charger disconnected.  It should be about 12.6 volts.  Leave it
disconnected from anything and let it sit overnight and check it again, it
should still be about 12.5-12.6.  Much less indicates the battery is going
bad.