My 2002 lancer wont hold a battery charge overnight

Sorry you spent to much money on replacing good parts. The ECM is bad. Not hard to figure out. If the alternator isn't grounded out the field inside won't engage. To many places will change the alternator and battery. Point and guess, is what I call it. If you paid to have it diagnosed and repaired, take it back and demand your money back.

Have the battery checked ! sounds like bad battery ! You can check the alternator by hooking up volt meter to battery , with vehicle running should see 13.1 to 14.8 volts if alternator is good ! How To Check Charging System EricTheCarGuy

OK, the problem appears to be the alternator is not charging. With a multimeter, check on the alternator output lug for around 14Vdc when the engine is running. This same voltage should appear on the battery +ive terminal. If not,
1. Check that the multiwire plug in the alternator does not have any damaged wires. If so repair the damage.
2. The 5mm wire from the alternator to the battery runs under the radiator, and can get damaged. This wire runs into the main fuse box on the RHS engine bay. There's also an 80A fuse (BOLTED in place) in the fuse box. Check this fuse is not blown, replace if needed.

how old is the battery

This problem may be a drain or a bad battery or alternator.

The first thing to do before going on trying to find the system that is draining the battery would be to have the battery tested and charging system tested.

A weak battery will seem ok after the car is jumped or will barely start the car and the alternator will charge it even though the alternator is overworking due to weak battery and during the day or when car does not sit long it will seem ok. then when car sits overnight or a few days battery will weaken on its own, making it look like a drain,

so first step is battery test and alternator/charging system test.

There are few possible reasons why battery is not holding charge.May be its weak battery or there is loose connection between battery to alternator.There are few troubleshooting help links,related directly to these types of problem,with there troubleshooting procedure.--------Click the link below and go through its troubleshooting details to resolve the issue:---Car battery loosing its charge overnight? http://schematicsdiagram.blogspot.com/2011/11/car-battery-loosing-its-charge.html
--------How to troubleshoot car battery?

http://schematicsdiagram.blogspot.com/2011/06/how-to-troubleshoot-car-battery.html

-------------
After replacing Alternator, the battery indicator light Comes ON dash? http://howtobyme.blogspot.com/2011/11/after-replacing-alternatorthe-battery.html
----------1998 Ford F150 pickup Battery Drains overnight due to Alternator? Alternator drains car battery? http://technoanswers.blogspot.in/2012/02/1998-ford-f150-pickup-battery-drains.html---------- 2002 Ford Focus sits over night and battery goes dead? http://technoanswers.blogspot.in/2012/02/2002-ford-focus-sits-over-night-and.html----------- Charging system problem on Chrysler LHS car? http://technoanswers.blogspot.in/2012/02/charging-system-problem-on-chrysler-lhs.html
-----------Toyota Corolla: Battery Drains out? http://howtobyme.blogspot.in/2012/05/toyota-corolla-battery-drains-out.html--------- 1999 Ford Taurus: Battery not holding Charge? http://whoisbyme.blogspot.in/2012/06/1999-ford-taurus-battery-not-holding.html
-------------How to Inspect Car battery? http://repairhelpcenter.blogspot.com/2011/12/how-to-inspect-car-battery.html------------ How to Test Car Battery? http://repairhelpcenter.blogspot.com/2011/12/how-to-test-car-battery.html--------- Car Battery Servicing? http://repairhelpcenter.blogspot.com/2011/12/car-battery-servicing.html--------- How to Replace Car Battery? http://repairhelpcenter.blogspot.com/2011/12/how-to-replace-car-battery.html-------- How to Inspect Car battery Terminals? http://repairhelpcenter.blogspot.com/2011/12/how-to-inspect-car-battery-terminals.html---------- How to clean car Battery terminals? http://repairhelpcenter.blogspot.com/2011/12/how-to-clean-car-battery-terminals.html---------- How to Replace Broken Car Battery Cables? http://repairhelpcenter.blogspot.com/2011/12/how-to-replace-broken-car-battery.html
--------------These details and procedure will help.keep updated for more help.Thanks.

Go through few Alternator related solved Solutions including replacement of alternator.Select and Click the link below:----How to replace alternator? http://schematicsdiagram.blogspot.com/2011/12/how-to-replace-alternator-on-gmc-sonoma.html
-----------------
How to test alternator on Dodge Stratus?

http://technoanswers.blogspot.in/2012/02/how-to-test-alternator-on-dodge-stratus.html

----------------
How to test and replace Alternator on Audi A4 Car models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-test-and-replace-alternator-on.html

-----------------

How to Remove Voltage Regulator on Car?

http://vwrepairhelp.blogspot.com/2011/11/how-to-remove-voltage-regulator-on-car.html

HOW TO REPLACE AN ALTERNATOR BELT

http://schematicsdiagram.blogspot.com/2011/08/how-to-replace-alternator-belt.html

---------------

How to monitor Vehicles charging system? http://repairhelpcenter.blogspot.com/2011/11/how-to-monitor-vehicles-charging-system.html

----------
Car Alternator making noise? http://repairhelpcenter.blogspot.com/2011/11/car-alternator-making-noise.html

-----------
After replacing Alternator, the battery indicator light Comes ON dash?

http://howtobyme.blogspot.com/2011/11/after-replacing-alternatorthe-battery.html

----------

How to inspect Vehicles Alternator?

http://repairhelpcenter.blogspot.com/2011/11/how-to-inspect-vehicles-alternator.html

---------

How to Test Vehicles Alternator?

http://repairhelpcenter.blogspot.com/2011/11/how-to-test-vehicles-alternator.html

---------
How to Service Vehicles Alternator?

http://repairhelpcenter.blogspot.com/2011/11/how-to-service-vehicles-alternator.html

How to Replace Alternator? http://repairhelpcenter.blogspot.com/2011/11/how-to-replace-alternator.html

-------
Alternator testing? http://schematicsdiagram.blogspot.com/2011/12/alternator-testing.html--------- Cars electrical system is pulsating? http://technoanswers.blogspot.in/2012/01/cars-electrical-system-is-pulsating.html------ 1998 Ford F150 pickup Battery Drains overnight due to Alternator? Alternator drains car battery? http://technoanswers.blogspot.in/2012/02/1998-ford-f150-pickup-battery-drains.html------- 2002 Ford Focus sits over night and battery goes dead? http://technoanswers.blogspot.in/2012/02/2002-ford-focus-sits-over-night-and.html--------- Charging system problem on Chrysler LHS car? http://technoanswers.blogspot.in/2012/02/charging-system-problem-on-chrysler-lhs.html---------- How to replace alternator 1997 Dodge Stratus? http://technoanswers.blogspot.in/2012/02/how-to-replace-alternator-1997-dodge.html------- How to replace Alternator on Mitsubishi Lancer http://www.howtorepairguide.com/2012/10/how-to-replace-alternator-on-mitsubishi.html
---------

These details will help.
For more help.Keep updated.
Thanks.
--------

Battery is to weak & not holding charge. If the battery does not have enough power the starter will make a fast clicking sound or you will just hear one click.

If alternator and battery is good, check the ground cables from the battery to the motor and frame grounds.

Sounds lie the battery is not getting charged by the alternator. If you slow charge the battery overnight and it retains a charge for a while then eventually dies, it may be good and the alternator needs to be replaced. If the battery does not hold a charge, you will need to replace the battery and have the alternator tested to see if it is faulty.