Forum Discussion

burlmart's avatar
burlmart
Explorer
Apr 19, 2014

Do all size 78 engine batteries mount identically at base?

Our MH is over 9 years old and its original AC Delco size 78 side terminals batt has been on life support for some time now. Overnite shore charging before a trip allow it to start engine and even do so a few days later, but it drops off to 10V soon after. I hope to take it out and go to our soon to open Costco for a new one. Do all 78 batteries mount to the truck via front and rear chocks/clamps which hold down a lip at the battery's base and loosened by a single nut? That is what I think I am looking at on out 6.0L Chevy.


Any other info and thoughts on the Costco size 78 batts would also be appreciated.
Class C
  • grandpaswagon's avatar
    grandpaswagon
    Explorer
    Apr 20, 2014
    Been using Costco group 78 for many years on several GM cars with no problems. Every one has had the mount as you describe. Which is not to say all 78 types from all makers must be that way, but Costco is. I have never seen a 78 battery not that way.

    Good value with 36/100 warranty.
  • Matt_Colie's avatar
    Matt_Colie
    Explorer II
    Apr 20, 2014
    The short answer is - YES.

    A complete answer follows.
    Vehicle batteries are described by an SAE group number. For a battery to be sold as that group (like 78), it has to able to be installed and retained as that group number describes. If a battery is listed as more than one group, it must be capable of meeting all the criteria of all the groups it claims to fit.

    Matt
  • j-d's avatar
    j-d
    Explorer II
    Apr 20, 2014
    What Matt said.

    Just beware of one twist - In a few battery "Groups" the Terminals can be switched, where the "+" and "-" terminals of the Replacement are on opposite ends from the Original. Probably not in Group 78.

    We don't have a Costco membership but we do have Sam's Club. Batteries are one of those things you seem to have to shop every time you need one. We were getting vehicle batteries along with RV "House" batteries at Sam's. This last time it turned out WalMart was the better deal, at least for Chassis batteries. Then we needed a House battery right at the start of a trip and it came out WM again. Sometimes one from an "auto parts store" worked out better but not so much lately. Prices centered on $100, no-cost exchange, 3-yr on Chassis and 1-yr on House.

    EDIT - The "Groups" are set by a council called BCI (Battery Council International) and this is their BCI Group Chart. The GP78 has only one terminal layout. It was the GP24 and GP27 that I remember getting jammed up on.
  • burlmart's avatar
    burlmart
    Explorer
    Apr 20, 2014
    For someone that rarely uses RV w/o shore or genset AC current, do you suppose this powerful group 78 from Costco batt would have enough amp-hrs to handle minimal DC needs other than starting the genny?

    It would be nice to have a low/no maintenance batt in the coach, and having identical type and age batts might prove a plus.

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