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My battery has been dead two mornings in a row. Both AutoZone and Advanced Auto have checked the car and they both say the battery needs to be replaced. Can I just unhook the old battery and put in a new one? I have heard that the whole car will have to be reprogrammed unless I provide a backup voltage via the cigarette lighter jack.
 

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The only thing that you need to do is clean around where the old battery was before putting in the new one, since you can never reach in there while the battery was in place. The car will run fine once the new battery is in, it will re-learn the optimum run settings once you start it up again, just let it idle for about 5 minutes or so. You will have to reprogram your radio settings and stations.
 

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There will be no adverse affects to your car from just taking out the battery. And on a side note you wont lose your radio presets either. The radio will default to 88.9 or whatever but you dont lose your presets.
 

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Thanks for the info guys.
you might end up clearing your ecu, which is fine, the car might run and idle a little weird as it relearns the info!!
 

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Clearing the ECU's adaptive fuel strategy settings would be fine. Clearing the ECU would not...[poke]
I think I understand what you are saying but could you please elaborate for the OP
 

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My Focus is a 2012 SE hatchback, is there anything special to restarting the computer systems on this model Focus? Everything was running fine but I noticed corrosion on the negative battery terminal. Hooked up a "memory keeper" then disconnected the cables, pulled the battery, cleaned it all up, reinstalled. Went to disconnect the memory keeper, the connection had come loose! But all the standard battery connections are now good, 12.4v on the battery. Got in the seat and all looked normal, little lights and mini flat screens were available. Turned the key to start and everything went dark. I got out and made sure nothing fell off! All still snug, put ohmmeter across connections they're all good, battery still at 12.4. Is there some factory anti-theft or something that disables the car? Some magic code to restart it all? Found nothing in the owners manual about this. Help?
 

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The terminals can be tight by the bolts yet loose when you grab them and twist. Crap terminal design. Cleaning the terminals/posts can remove some material which makes that worse too.

Have the battery checked, simply having voltage is not enough if the 12.4 drops to say 10 when you switch to starting the car.
 

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Thanks, AMC49. While waiting I found a thread on the ST forum ( Reset ECU ) and another bit of advice on youtube (
) that got me going, too. But it still seemed nothing was working. I did what you suggested AND what those suggested and thinking of what you said about voltage drop during starter engagement AGAIN cleaned all the terminals and reconnected all SNUGLY (but not uggggggg tight) and whaaaaalaaa it works. Thank you!
 

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Hi!
Small side not to add to the end of the discussion, my 06 SE w/ around 80k miles had an alternator go bad a few years back and I was experiencing similar symptoms.
 
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