how its going now?
BTW did mechanic told you that how much volts of battery are? because if there is plus/minus 1 volt, then it still brings no issues in starting. But if the voltage are 10 or less at idle state, then it can be a problem.
some people check battery voltages before starting & after, with head lights on & off, with AC on & off.
Then they take final observation that either the battery will stay or should replace.