Ok, New here and rookie mech....I got Service Engine Soon light the other day
engine was still running OK...drove home from work parked it went to bed....went to start this morning and battery was flat dead...10.5 Volts.....charged battery all day still dead... exchanged battery.....restarted engine and stalled after 4 starts engine running fine and no Service engine....I understand the codes were reset during battery being disconnected and changed...my concern is I had no indication the battery was bad (no slow crank etc) is this possible the service engine light came on because of battery failure?...the battery light never did come on....going to drive for few days and see waht happens....this is a great site glad I found it....
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rookietech

The ECU is not programmed to detect a bad battery but it will detect a bad alternator. Service engine light will come on because the reference voltage on all sensors just changed. You end up having something like 20 error codes which doesn't make sense. I've had this problem with other vehicles but not my Outlander(I love my Outlander) 10.7 Volts indicates one bad cell out of 6 and definitely a battery problem. Engine stalling for first 20 minutes after battery replacement is a normal possibility. The last time I had my timing belt changed they disconnected the battery and my Outlander stalled a few times at STOP signs until the ECU remapped itself. Batteries do fail especially if you live in a 4 season environment. My wifes car is 10 years old and it is on it's 4th battery and it's 4th alternator for that matter and these seem to fail on the day where it is -20C.

Thanks....seems to be OK today ECU must have remapped....still strange why Service Engine came on...alt is producing 14.5V while running....guess it's wait and see...
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rookietech

The alternator will not give you 14.5V at lower RPM and will actually stop outputting current.

Outy...my alt is reading 14.5V at 2000 RPM...and the dead cell just came from out of the blue....do you know the correct output for the alt....wondering if alt cooked battery....it was only 10 months old.....
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rookietech

14.5V at 2000 rpm sounds about right. Even if your batterie was only 10 months old it could fail. I've seen some that fail the first day. Some last 10 years or more. Luck of the draw. New fully charged batterie with engine off should read between 12.1 and 12.7 with no load (nominal is 12.45Volts). About 2.1 Volt per cell times 6 cells. This is why you were reading a little over 10 volts when you lost a cell. ECU will not detect bad batterie but will give you all kinds of random codes because voltage on sensors is out of wack, then service engine light comes on.