Will Disconnecting a Car Battery Reset The Computer? Disconnecting the battery for a short time may not do the trick because the car's computer, or ECU, still has some current in it. Waiting for over 15 minutes after disconnecting the engine will help ensure the equipment is reset
However, if the ECU is unplugged, it will retain any charge it may have even if you create a power draw someplace else in the vehicle. So you'd need to wait a decent amount of time to be "sure" it's drained. Some folks go so far as to unplug the battery and let the car sit over night.
While disconnecting the battery will not permanently damage your vehicle's computer, it can cause it to function differently. That's because, if you disconnect your battery for long enough to reset the computer, it may cause the processor to forget everything it has learned .
Engine stalling or misfiring
Another symptom of a bad or failing ECU is erratic engine behaviour. A faulty computer may cause the vehicle to intermittently have issues such as stalling or misfires. The symptoms may come and go, and may not appear to have any sort of pattern to their frequency or severity
No, if done correctly it will not damage either battery. However, there are a few things to note. First if your battery was fully discharged it will have a shorter lifespan due to build-up between cells. Second, if the jump is done incorrectly you can fry computers, fuses or electronics and yes even the batteries.
Let the dead battery charge for a few minutes, the longer the better, before attempting to start. This step is particularly important when boosting batteries that have been totally discharged in extremely cold weather. You can rev the helper car a bit during this time if you wish, then try starting the disabled car.