seems the voltage at idle is low, so battery is discharging when driving
around in traffic.
also voltage at 3k rpm sounds low,
If you have another car or friends, check voltages under the same
condition.
Try measuring same voltage with lights on.
You might have a bad alternater.
There might be more info on the web.

This is Turtle.

First the car idling normally and you can't get but 12.15 volts across the
battery. Well flate out your not charging the battery at idle speed. Bad
Alternator !

Secondly Running the engine at 3K RPM's and puts out 13.56 volts. You are
charging the battery enough if you run the auto at that speed all the time to
keep the battery up. Now when you start just getting 12.15 volts across the
battery at a igle your dischanging the battery or just running off the battery
and no help from the charging system at all. Bad Alternator !

Thirdly. The amperage draw on the system when the car is off and key is off. the
auto theif system and other protection device are running all the time and needs
power too. Now the .55 amps is pretty high for that system. The electric system
does need power to run the computor to keep up with problem and recording the
date and time of the problem. There is things that are still running when you
cut the key off. Bad Alternator !

To test the system to see if it is the alternator or the battery which is bad.
Here is how.

Take a volt meter on D.C. voltage and read across battery with the key off and
door shut. You should get 12 to 12.6 volts. [ If you have 12 volts -- you have a
week battery but still working. ] [ 12.6 volt or so --- a very hot battery. ]
Anything 11.99 volts or less you have a bad battery.

Then take the volt meter and read across the battery while it is running or
idling normally with most of the air and lights cut off. You should be getting
13.00 to 14.5 volts or 1 to 1.5 volts above the voltage reading you got from it
while everything was cut off and just reading across the battery atleast or the
least you can see and be good. Now most of the time you will see 14 volts or so
at anything out of a good alternator and battery.

If you need to discuss it e-mail me and talk about it.

TURTLE

charging appears insufficient.  drain of 0.1 is far too high..
A good battery will have 12.7 volts available (charged and left to stand for
a day or three)
check and charge battery, refit and check how much current is being drawn
with the alternator disconnected, should be a max of about 0.03, reconnect
alternator and check again, should be max of 0.03
the high initial draw when you connect the battery is common to most modern
cars.
if you are not getting over 13 volts at idle (with a good, charged battery)
then there is an alternator fault.  ls400 alternator faults are common,
particularly if you have had a leaking power steering pump.

mrcheerful

The drain of 0.1 A (100 mA) when shut down is way to high. This will be
enough to flatten a healthy battery in 3 or 4 weeks.

You need to try and track down what's drawing the current - as I said
originally, silly things like trunk lights, glove box lights are a common
source of this problem. Otherwise, it gets more expensive - could be faulty
alarm, radio etc. taking too much current.

That's about a full volt low. Should be around 14.2 to 14.4 at fast idle
with nothing turned on.

Again, about a volt low. I would expect around 13.2 to 13.6 at idle with
no load.

Your math is correct. Still a 100 ma static drain (to me) seems way high,
like a glove box light or similar staying on. Nothing in the vehicle's
electronics should have a 100 ma continuous drain. Remember with the hood
open you have an engine compartment courtesy lamp. I assume you're
disconnecting this when taking your measurements.

Alternator output (based on your meter) is out of spec. Static/standby
current drain is (also IMO) about 10X higher than it should be... again
per your meter.

At high idle with everything on (A/C blower motor, headlamps, glove box
open, 4-way flashers on, all doors open, trunk open, stereo blaring, and
someone sitting in the car operating the moon roof and power window
buttons & door locks, seat motors, etc. you should still see a battery
voltage of at least 12.0 to 12.6.  This "full load" test may actually tell
you more than the other tests you've done. In addition to alternator
problems, I'd start looking for poor or loose connections in the charging
circuit, between alternator and battery.

I thought I'd layout the procedure to check your battery and charging
system.  First, the battery has to be fully charged.  Then take a voltage
reading, which should be about 12.5 volts.  Next start the engine and the
voltage reading should go to 14.5 or so.  This tells you the alternator is
putting out.  The last question is whether it is putting out sufficiently.
So, turn on the headlights and see if the voltage stays about 14.5.  If so,
the charging circuit is OK.

Next you need to verify whether there is drain back from the battery when
the engine is off.  To do this, disconnect one of the battery terminals and
place an ammeter in series with the battery terminal and the removed cable.
There may be an initial surge of current, but should quickly stabilize to
less than 50 milliamps.  Make sure you close the car door and have all
lights off.  On some cars this reading can be as high as 80 milliamps, but
any higher than this will cause a dead battery after a few days.  If higher
you need to remove fuses one at a time or check for leakback through the
alternator.  Sometimes something as simple as a trunk light switch can cause
the problem.

Lastly, you need to check the battery to see if it can hold a charge and
whether it can provide enough power to start the engine.  To do this, again,
the battery must be fully charged.  Take a voltage reading (should be about
12.5).  Disable the engine so it will not start.  This is best done by
removing the fuse for the fuel pump.  Crank the engine for 5 seconds (use a
watch).  Wait 15 seconds and do again.  Repeat this several times.  You
should be able to do this 10 or more times before the battery goes dead.  If
it fails sooner, the battery is defective (assuming you don't have excessive
current draw problem with your starter).

Lastly again starting with a fully charged battery, disconnect either
battery terminal.  Take a voltage reading.  Wait 12 hours and read again.
Repeat this for two days.  The voltage should no drop more than.1 volt.
Reconnect the battery and crank the engine.  If it cranks, battery is OK.

John Ackerman
acker1820@charter.net