Battery discharging with ignition off - MustangForums.com



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Old 07-22-2018, 05:51 PM   #1  
68XR7
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Default Battery discharging with ignition off

whenever my 07base coup sets for over 3 days, I find that the battery is usually dead. I have charged it and had it tested. There are no dead cells, or obvious problems with the battery. There are no lights on in the car, or obvious problems like that. Somebody suggested a possible problem with the ignition switch. Any ideas for a test that i might try to help determine what the problem is?
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Old 08-14-2018, 07:28 AM   #2  
SilverStallion05
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Do you have any aftermarket electronics in the car? Does the car beep/chime when the door is open but the key is out of the ignition?
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Old 08-14-2018, 08:05 AM   #3  
Buckshot Barry
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I've had a Battery Tender Plus plugged in to my 2007 Pony Package accessory outlet since 2008. Problem solved.
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Old 08-14-2018, 02:07 PM   #4  
Derf00
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After it's been sitting for a few days, how far do you drive it before letting sit for a few more days? If you don't drive it for more than a few minutes before storing it, the battery doesn't get enough of a charge to last until the next time you start it up due to normal electronics draw when the car is off.

A battery tender is probably the best way if everything else about the battery is ok.
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Old 08-14-2018, 03:07 PM   #5  
08'MustangDude
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Mine sits a whole week, aftermarket radio, and other stuff that take power, like the
remote 4-chanel relay center; and the car cranks as fast as it does after I drove
it for a half hour.

My rear LEDs, all but two of them, even stay on, very dim, for about 8 minutes after I shut the
car down, sits a week, and STILL starts right up. Anytime I pop the trunk, the car wakes up
and those LEDs will be on again for another 8 minutes after I close the trunk lid. Car still starts
right up after a week.. I have left my trunk lid open for hours while working on the car during the
week, and come Saturday, starts right up.

You have to test for current drain, 3-days and a dead battery is not normal. I have
a 2015 Jetta TSI, it used to go dead after sitting three days, but that wasn't till
earlier this year when that started happening. Got a new battery, hasn't happened
since. It also has an always on Volt Meter, so I can check the voltage as soon as
I open the door.

After sitting for a day, a fully charged battery should read over 12.6 volts. If the battery reads 12.45
volts or less, it is low (less than 75 percent charged) and needs to be recharged.

Readings at 80 degrees-f
12.66v . . . . . . . . . . 100%
12.45v . . . . . . . . . . 75%
12.24v . . . . . . . . . . 50%
12.06v . . . . . . . . . . 25%
11.89v . . . . . . . . . . 0%

Battery voltage readings will drop with temperature roughly 0.01 volts for every 10 degrees-f.
At 30 degrees-f, a fully charged battery will measure about 12.588 volts, and at zero degrees-f
it will measure about 12.516 volts .

Some Fords, the electrical system will continue to pull as much as 850 mA (almost 1 amp) for
up to 20 minutes or more after the ignition has been turned off. Once the car has gone to sleep
mode, current drain should be less than 50 mA. If it stays high, then you have a device
drawing too much current.

Check for Voltage Drop: Use a digital volt meter to measure voltage drop across individual fuses with the key off.
This method does not require removing any fuses or disconnecting the battery. Set the voltmeter to the millivolt (Mv)
scale. No current flow through a circuit should show a zero reading on the voltmeter when the probes are connected
to both sides of individual fuses. Any reading other than zero (typically a few tenths of a volt) would indicate current
flow in a circuit and a potential drain on the battery.

Use an ammeter with an amp probe to measure key-off current flow at the battery: Connect an inductive amp
probe to your ammeter or digital multimeter, then clamp the probe around one of the battery cables. Set the meter to
read milliamps (mA). If there is a key-off current drain on the battery, the meter should detect the current. Make sure
the amp probe you are using is one that is calibrated to detect small milliamp currents, not large multiamp currents.

Use an ammeter to measure key-off current flow at the battery: This method requires disconnecting one of the
battery cables and connecting the ammeter in series between the battery and cable so any current flow will pass through
the meter. If you need memory retention for devices, then provide backup power to the electrical system before disconnecting
the battery. As before, use the milliamp scale.

If the current rating is higher than it should be, Remove and replace fuses and relays one at a time to find circuit that is draining
the battery. Or, use a voltmeter to check for a voltage drop across each fuse. A voltage drop reading would indicate current flow
in the circuit.

Sometimes a bad alternator diode can cause a car battery to run down. A shorted diode allows current to flow back to the
alternator.

Causes of excessive current drain from a car battery include things like lights that remain on (trunk and hood lights, interior lights,
brake lights, etc.) and also relays that may be stuck on, or modules that are not going to sleep or powering down. Keyless entry
systems and anti-theft systems can often be the source of a significant key-off current drain on the battery.

A fuel pump relay that sticks on may keep the fuel pump running after the engine is shut off. A switch or relay that powers a rear
window defogger can stick on, pulling current from the battery after the ignition is off. An electronic suspension module, ABS
module or keyless entry module may remain active long after it should have powered down.

An accessory such as a DVD player, game console or cell phone charger left plugged into a rear seat power receptacle may be
pulling power from the battery. So before you spend a lot of time trying to figure out where the amps are disappearing, Check all
of the vehicle's power receptacles to see if something is plugged in that may be using power, though, I leave all mu charging items
plugged in, and the battery is fine. I have replaced the front 12V power point with a dual USB charging port, and it's on all the time,
after a week, car starts fine. Battery makes all the difference, and the type you use. I will always replace the battery with one
that has higher CCAs, and higher reserve capacity, AGM if I can find one on sale.
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