This is a great question. Technically yes, a loose battery connection can
cause a visual smog check failure. Though the battery is not directly an
emissions component it is part of the vehicle's emissions computer system.
Based on the technician he or she may note it as an emissions system defect.
It's a grey area and we recommend you simply repair this fault before
getting a smog inspection. Plus this problem will prompt a smog technician
to be more cautious when performing the visual inspection to ensure there
are no other emissions tampers or defects.
Also make sure your vehicle has uninterrupted battery power for at least one
week of regular driving. Power interruption to the Engine Control Computer
will cause your vehicle emissions "readiness flags" to reset. This will
cause a smog check failure. Only one to two weeks of regular driving will
set the flags again.
