The Addicks punished Bournemouth's wastefulness in front of goal when Kermorgant pounced on Danny Green's corner to steer the ball home deep in time added on.
Bournemouth went close to taking the lead when Donal McDermott found space down the left channel to cross for Wes Thomas, whose shot cannoned back off the post.
Charlton took the initiative after the break and Green forced a sprawling save from Bournemouth goalkeeper Darryl Flahavan following Johnnie Jackson's quick free-kick.
Danny Hollands was the next to try his luck for the rejuvenated visitors, with the former Cherries favourite striking narrowly wide.
Bournemouth could have taken all three points in injury time when Harry Arter skipped past three defenders, but he lacked composure and fired wide.