This is the most comprehensive listing I’ve seen:
Layne explained what the R means. A group number followed by the letter “R” means the terminals are reversed* when facing the battery with poles at rear of the battery from you, the Neg pole is on right.* If there is no R following the group number the negative terminal is on the left.
Hi Dennis, it’s not just the size that matters, but the cranking amps which is the most important…
I do understand that but I have found that most batteries of that physical size seem to have enough
Dennis
Lots of these mentioned battery’s will work ,lower batteries go in past the heater motor easier. I think group 35 is amore common size ( battery)and therefore cheaper fits fine on my car
Yeah, that big Optima was a pain. The Group 26 much easier fit in and out, and plenty of amps.
I learned about batteries when I had a big boat 
could have flown in a lot of cold beer for what I spent on batteries. In a nut shell they have so many amp hrs in them from new . If they discharge more than 25% their life is reduced so you want to keep them above 75% for best life That’s their sweet spot .
Discharge them more and suffer accelerated battery degradation
If I get 7 years out of a battery I’m happy 
it’s hard on alternators running weak battery’s
I’ve load tested battery’s
Used a hydrometer
Charged them
Ready to go all good
Come to use the car a month later …dead …
Batteries seem to last 3-11 years luck of the draw Ymmv
Cheers
Thanks to all who offered suggestions for an E type battery… It seems a bit of a mine field. Group 26,25,35 and 58 were mentioned as being OK. On my '70 series 2 OTS the battery terminals are on the top of the battery and the battery is installed to that the terminals are on the outboard side. The positive terminal is on the right and the negative earth terminal on the left. Whether this is original for my car I don’t know . Some of the photos on this topic showed the battery installed with the terminal on the inboard side.
Same here. That’s why you need an “R” like my 26 R or other R. For ease of in and out and fitting while installed get a smaller battery with adequate CA or if using in a very cold climate pay attention to the CCA.
Lots of battery charts around that give you the size of the various groups, or call a good auto parts store and tell them you want a smaller sized battery in an R configuration with good CA. I think my mid level Interstate Grp 26R has 550CA and it’s alway been plenty. But then I’m not cranking up at Christmas in Chicago either.
hmm. ok, so is the battery supposed to have the neg pole on the right? Because the ground is over on that side. But then the positive hook at VR is also at the right.
Sounds like the setup on my 1970. I replaced the battery cables but kept that arrangement. I also put a red rubber booty on the positive terminal. I dropped wrench on a 12V battery once. It was very ugly.
Bill, the 26 R places the Neg Pole on the left with the terminals to the outside edge of the car when viewed from the outside looking down at the battery. If the poles are away from the outside of the car the neg is on the right.
I may be wrong but I believe it is correct for the terminals to be on the outside edge of the car rather than the eng side. The outside pole position with an R battery places the + pole next to the buss by the Regulator and the - Pole next to the wheel well with a clear line to the chassis ground on the foot well. I moved my ground to the engine for better grounding. Additional chassis grounds are added from eng to chassis.
For my '69 OTS my existing battery (now dead) is an Optima 25 (reverse mounted, and not using any bracket). The 25s and 35s appear to be same dimensions. Anyone have any luck using the stock bracket (6 13/16" x 9 15/16")??
Brian,
If you look further up in this email string to my post from June 2022 you will see that I installed an Interstate Group 25 size battery in my 1969 E-Type FHC with the correct bracket, clamps, wing nuts, and washers. I also included a picture.
Paul
Brian,
Here is a more recent picture of the Interstate Group 25 battery in my 1969 E-Type FHC after I installed a quick disconnect knife switch on the negative post to make it quicker and easier for me to disconnect the battery when I work on my car.
Paul
Thank you Paul. As it turns out I went with a 25. My Interstate supplier was out of stock, but NAPA Auto Parts came to the rescue. The fit doesn’t look as tidy as yours, but it works.
which battery has the highest cranking amps and longest warranty?
also my alternator crapped out after a yr. whats the highest output an orig alternator can be upgraded.
Cranking amps? Were you planning to use this as your winter car? Battery warranties have been getting shorter of late, prices much higher. I think most brands offer 3 yr warranties, prorated, which may as well be no warranty.
There are a lot of considerations with upgrading the alternator. If your '69 has a reverse mounted alternator, any replacement has to either have an omnidirectional fan or a counterclockwise fan, which limits your choices. You can “amp up” as much as you want, but there’s really no reason to go very high. At peak, all the car’s systems together draw about 50 amps. Which means the alternator can be straining at idle on a very hot day. Going to a 70 amp alternator would get you adequate headspace. Much more than that is just a waste. I’m currently running this;
Contrarian here…I use a small small group 26…some $69 from walmart (was $48 then 58) why…well a good running E with Strombergs, manuel choke set correctly is very easy to start…so is a miata, spitfire, tr4, tr6, mgb, xj6 even a 1st gen cummins with VE Pump…On the gas car collection I much prefer a little starter fluid and a sqirt bottle of gas to prime them…
I see my collection, of batteries, is getting a little long in the tooth"…3 from 2016 and the newest 2020…off I go to Walmart
Lugging a group 26 from car to car is a breeze compared to say a group 31 (what a 1st gen Ram Cummins uses)
Works for me
Mitch
PS. been hunting 4 months in the high country of Colorado…burr…got too cold for my old bones…march on
