Group 24 was the base battery size for every Chrysler product, back then, IIRC. Group 27, which is larger was optional.
Group 24 is physically smaller and has less power and reserve power than a Group 27. When time comes for replacement, "bigger can be better".
Reasoning always appeared to be that with the larger B/RB engines, generally 4 headlights, a/c, and other power requirements on the system, the Group 27 would be better and allow the car to operate best. Might even decrease the amount of discharge at idle at night, at a stop light. And, of course, a "big car needs a big battery"? So that's what I always bought and gladly paid the higher price, knowing it was "the best" I could get.
In modern times, with advances in basic battery technology (and sealed batteries), newer versions usually have more power than they did back in the 1970s. Which means a physically smaller battery CAN have more power than the older, larger batteries did. As in a Group 24 battery can have more power than a prior Group 27 battery. You can find the OEM specs for them in the appropriate Chrysler factory service manual or in the sales order guides at
www.hamtramck-historical.com .
As to cable post positions, the difference between a 27 and 27F battery is that the terminal positions are switched for FORD applications on the 27F. For Chrysler and other normal applications, when the battery posts are on the "firewall side" of the engine compartment (not the "core support side", the negative post is nearest the engine, so the ground cable goes to the first lh side intake manifold/a/c bracket hold down bolt. On the 27F and 24F Ford applications, the positive terminal is nearest the engine, reversed from the normal 27 and 24 applications.
Generally, the more months of warranty and "free replacement period", the more powerful the battery, in any size. Your judgment call on that. Which can mean that if you use the car a lot and daily, leaning toward the more capacity might be best. If you suspect the vehicle might sit a lot, DO get some sort of trickle charger to hook up to it as a run-down battery is NOT generally a cause for warranty replacement (unless the battery has failed internally and will not hold a charge, after charging for several hours).
Be aware, too, that in the "free replacement" orientation. There is only ONE warranty. That one starts with the purchase of the battery itself. Any replacements under that warranty do not extend the basic warranty period. In other words, the initial warranty does not start over with each warranty replacement. Be sure to verify that in the battery warranty documents!
ONE last thing, keep the sales receipt in a safe and COOL place, in some sort of compartment. When all I could afford was WalMart batteries, the clerk would suggest using some clear, wide tape to attach the sales receipt to the battery itself. Sounds reasonable in order to keep up with it, right? UNTIL you later realize that being (generally) a "heat print" paper receipt, the engine head faded the images on the receipt, making it unreadable. Which basically renders the battery unwarrantiable. Only possible saving grace is the "burn code", usually hidden under a label, but possibly in plain sight, which is the production date code (month and year) for the battery. All must have them, I believe. But finding an employee who knows what that is and can then decipher it, might be a trick?
The old pro-rated warranty has been replaced by the "free replacement period", so keep and COPY those receipts . . . safe, FINDABLE, and cool!
Sorry for the length,
CBODY67
