my 2003 alt will barely move after jumping mechanic said alternator was bad on 2003 Nissan Altima

the problem has occurred twice had it towed to a shop who got it started and ran fine after that he said the alternator was bad had it checked but was told it was ok had to jump it again it barely moves when in drive

Asked by for the 2003 Nissan Altima
2 more answers , 4 more comments
How old is the battery? Has it been tested? No bad cell(s)?
its good its only 3 months old
How was it tested? Even new batteries can be defective!
alternator and charging system was tested on a machine
Starting wityh a fully charged battery(assume 12.5 volts) turn on the high beam headlights (engine off), and let it sit for twenty minutes and re-test the battery.Might show a bad cell.