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TR2/3/3A Need New Battery for TR3A


After more than 17 years - my red top Optima battery finally gave up the ghost. Looking at purchasing an Interstate battery from Costco (based on all the positive remarks about that brand of battery on this forum). My TR3A has been converted to Negative ground. Which size battery would be best - the 24 or the 27? Or, should I just go with the larger size battery (the 27) because it has greater cold cranking amps (810 versus 700)?


Country flag
I'm of the school the bigger the better. I get a minimum of 6 years out of a battery. If it fits - use it. What's the downside?

Lou Metelko

Jedi Trainee
Based on your 17 year service from the Optima Red Top it is the least expensive on a cost per year basis. The battery tray on all the TR2s through the 4A were designed for the group 27 size. Only problem with the 27 size is the hoisting the back breaking task of putting it in place. Any other size just does't look right to my eyes.

Peel off the Interstate or what ever stickers and replace with a Lucas 4" X 6" sticker from any of our suppliers.

Lou Metelko
Auburn, Indiana


Jedi Trainee
Country flag
I went in a weight reduction kick when it was time to replace the battery of my TR4 in 2008.
I looked around and settled on the Group 59 Costco battery used in V6 Ford Mustangs and saved 16.4 lbs over the Group 27 battery. That Group 59 battery is still going strong after 12 years.

For comparison:
Group 59, 590 CCA, 32.6 lbs
Group 24, 700 CCA, 42.1 lbs
Group 27, 810 CCA, 49 lbs

Yes, I gave up some CCA, but in my climate that is not a problem even using 20W-50 oil in the dead of winter (I do have a high torque starter).
The only thing I had to do, to fit the Group 59 battery in the TR4, was shortening and cutting some longer threads on the "J" bolts since the battery is that much smaller in size.



I have negative ground. Positive side of battery needs to be on the left - does it matter is the battery posts are located toward the front of the car - or, toward the back (firewall)?


I have negative ground. Positive side of battery needs to be on the left - does it matter is the battery posts are located toward the front of the car - or, toward the back (firewall)? Interstate battery group 24 and 27 batteries posts are located differently. The group 24 would have the battery posts facing the front of the car (toward the hold down bar) - the group 27 battery posts would be at the back of the battery box (next to the firewall) - these two different installs would then place the positive post on the left hand side where the positive battery cable is located.


Jedi Trainee
Country flag
I also have negative earth on my TR4.
I personally liked the idea of moving the battery posts away from the firewall and toward the engine. I also installed a battery cut-off on the negative terminal for convenience. https://mossmotors.com/switch-battery-cut-off-1
Attached is a pic of the Group 59 battery installed in my TR4, battery posts are toward engine, neg post is at the left side.



  • TR4 1963.jpg
    TR4 1963.jpg
    81.1 KB · Views: 51


Jedi Knight
Country flag
I use a Miata battery in my TR4 as part of both the car and owners weight loss program. The car has alternator and an electric cooling fan that runs after shut down. No problems yet
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