"The Caped Crusader Caper" is the 2nd meeting between Scooby-Doo and Batman, airing just before Christmas 1972.
Mystery Inc. and the Dynamic Duo team up again to rescue absent minded Professor Flakey (Don Messick) from The Joker (Larry Storch) and The Penguin, who seem to have escaped since their last appearance.
Edit: 6/15/18: The original video was deleted by Dailymotion. This excerpt will suffice for now.
As we've documented, it would be nearly 40 years before the two teams would meet again, this time on Batman: The Brave & The Bold, with Weird Al Yankovic thrown in for good measure, and just two years ago, they met in the pages of Scooby-Doo Team-Up, with the gang meeting two different versions of Robin (The Teen Titans Go! edition appeared in issue 4, while the one the gang knows was in issues 1-3 & 6).