Battery draw

[rhughes@domain.elided]

   >>First of all let me apologize for the length of this but i feel  it is
   necessary to be very  specific so I  can get the correct answer.

Don't worry.  It's better to get all the info in at once than to keep
adding info with new posts.  You ever notice how telling someone about your
car problems is like going to the doctor?  You want to tell them
everything, but you're not sure what matters and what doesn't.  I've always
felt that a good mechanic or parts person or doctor should listen to
_everything_ the "patient" has to say.  At any rate...

   >>I have a 71 Scout II that has a significant battery draw, i.e. if I
   leave it overnight it is completely dead in the morning.  I tested the
   battery and it is good, no dead cells and there is no drain if I
   disconnect the positive battery cable from it when it is not in use.  I
   borrowed a voltmeter from a friend and hooked it up to the battery in
   the following manner:  I removed the positive cable from the battery and
   hooked up the positive lead from the tester to the positive terminal on
   the battery and the negative terminal from the tester to the positive
   battery cable.  Having done this I got a reading of 10 volts on the
   volotmeter which, I'm lead to believe, means that there is a 10 volt
   draw on the battery.  I then pulled all the fuses one at a time and
   checking the voltmeter
Charlie, in my experience, testing battery draw is done differently.
Instead of unhooking the positive cable, you need to unhook the negative
cable.  Hooking up your meter as you describe doesn't test draw, it tests
voltage.  The unhooked positive cable is essentially now the negative
battery terminal, since there is a circuit between the neg terminal, the
neg cable, the engine block, the starter, and the positive cable.  Try
putting the positive lead to the positive terminal and the neg lead to the
neg terminal, and you'll probably get a reading of 10 volts.  That's pretty
low for a battery just sitting there, with no load.  A twelve volt battery
should read somewhere around 12 volts, and shouldn't drop below 10 or 9
when you crank the engine.  You can test that yourself, by touching the pos
lead to the pos terminal, and the neg lead to the neg terminal, and having
someone crank the engine (you might want to disconnect the dist so the
engine doesn't start).  Better yet, take the battery to Checker or Autozone
and have them do a load test, which is essentially the same thing repeated
a few times.  They can tell you for sure if your battery is toast, and
frankly, that's what I'll bet is going on. It's not that the battery is
being drained, it's that it can't hold a charge.

Still, you may indeed have a battery draw with the ignition off.  The easy
way to test this is with your multi-meter (I assume your friend's meter
tests amperage as well? If not, go get one -- a Digital Multi Meter is
invaluable).  Unhook the _negative_ battery cable from the terminal and put
you ampmeter in series between the cable and the negative terminal.  This
will tell you how much current is being drawn through the circuit and back
to the battery with the ignition off.  If you have a stereo with preset
stations and a clock, it will draw a tiny amount of current at all times.
Mine draws about 17 milliamps when functioning correctly, which with a good
battery is fine.  You'd only need to worry about that much current if you
were leaving the truck for weeks.

Recently, however, I hit a bump and some wires inside my dash shorted,
causing some strange problems with my stereo.  The next morning my battery
was dead (voltage 9.something), and when I hooked up the ampmeter, it read
235 milliamps.   Apparently that is enough to kill a battery overnight.  A
better/newer battery would probably have held up longer.  I jumped started
the truck, charged the battery to 12 volts, and two hours later it was dead
again.  I unhooked the stereo, had Checker test the battery (it was
trashed), and bought a new NASCAR Select battery with 875 ccas (cool,
NASCAR!).  No problems since, but at some point I need to go into my dash
and figure out where my wiring went bad.

Anyway, here's what I would do:

1.  Test the battery draw with an ammeter between the neg bat cable and the
neg terminal.

2.  If it is low (say below 30 milliamps, but that's a guess based on my
limited experience), then have the battery checked again.

3.  If it's high (over 30 milliamps?), have the battery load tested anyway,
just to eliminate the possibility, then
start looking for the battery drain (the way you were unhooking stuff
before would probably work), but with the ammeter hooked up as noted.

If I've written anything vaguely inaccurate or flat out stupid, I'm sure
someone will correct me.  Otherwise, good luck, and feel free to email me
if you want to.

Rob