"group #" is the term used to identifiy batterries of different sizes and the location of their posts. Group 78 batteries have side terminals, which are only used on GM vehicles. group 34 has top terminals. the red top optima 34/78 has both the top terminals and the side terminals, because they are made to fit a variety of cars,...preludes require a group 24F, optima doesnt make a group 24F...however, it can be substituted with the 34/78 since the terminals are on the same location and is fairly the same size as the group 24, and of course the optima's CCA's (cold crankng amps) exceed those of the regular group 24F.