So I know batteries come in all sizes shapes and forms but what the consequences on a size for a nostalgic flathead powered roadster with no bells and whistles? I need to build a battery box for my T roadster project and it will live in the trunk. I would like to use something that a guy can get anywhere you are in your travels. What’s a dimension that doesn’t take up much room that a guy could find in every town where ever ya go?
I'm on my phone so it's not very convenient to look up physical dimension sizes but I've read before that it takes one cold cranking amp per cubic inch of the engine. I've used that recipe on several cars now and have never had a problem with inadequate cranking speed. Now my my applications have always been lower compression engines probably 9.5:1 or maybe less so something with high compression let's say 10 and 1/2 might need more than one amp per cubic inch. Lynn
Group 24 was the most common 12v in the older days, and is pretty easy to find, and several other sizes will fit in that hole. If you make a smaller place for it, might not be as easy to find what you need when you need it. Although 26R works if you want to save some room/weight. They're pretty easy to find (walmart, etc)
35 group size is decently compact and should offer enough cranking power for most applications. Depending on the economy-premium you can buy just about anywhere will give you different cca and reserve capacity. Most the time you look up a battery application for older or "universal" they show a 35/75 which will give you top and side post. I could be wrong as well but I think that's the sizing for most your cheap off the shelf plastic battery box size. I'd say your most common sizing as well.
Battery size chart: https://shop.advanceautoparts.com/r..._content=404739&c3ch=Affiliate&c3nid=IR-27795
Might correct myself in I think most battery trays are a 34/78. I'd agree with squirrel as well on 24. Depending on size and cca ifs it's real tight a 51 is used in most Hondas that I recall and is also pretty common. Good luck on a 51 if you need more than 600cca though, I believe that's where most max out in that group size for a premium.
Following this thread! Looking at the same situation on my 31' tudor, space at a premium. Looking for something small, possibly under floor mounting. ..
I’ve been running an Odyssey PC680 battery in my roadster for years. You won’t get anything smaller. Just installed one in my coupe .
I pick up trays from shoebox Fords when I see them at swap meets. They have easy mounting edges, built in notches to hook the side hooks into, and fit common size batteries. But I don’t know what that group number is off the top of my head.
24F for me. Fit most everything, although the post are reversed from type 24. Might matter to you, might not.
Get one for a Honda with at least 500cca. There’s one in the truck of my son’s 40 Chevrolet. The engine is a 310 GMC 6 with 10-1 compression. Hondas are every where..
Apologies for the tangent, but this was very nearly a serious rabbit hole for me earlier this year. I'd heard about combining batteries with supercapacitors in other contexts, and subsequently came across devices advertised for emergency car starting, which use residual charge in a pretty-much-flat battery to charge a supercap. It got me to thinking that, for a very basic electrical system, having something on this principle hard-wired into a car could allow a really tiny, simple, low-tech battery to be used (I was thinking NiFe — early 20th century tech). Supercaps are well after our era (late '70s) but it struck me that they could make the most marginal of "traditional" electrics a lot more viable.
I run this tray from Speedway. I lopped the side mounts off it, mounted it to my inner fender with carriage bolts. My buddy is an Exide dealer, I use a 24F in it. https://www.speedwaymotors.com/Cust...MI7rftp_X6ggMVGlBHAR3T5AZsEAQYAiABEgJOvPD_BwE
Doesn't the F mean Ford, so the posts are reversed from all the batteries that don't have the F after the group number?
I believe it means flat top, if you look at a 24R they have the caps that protrude over the top instead of being flush like the 24F.
Since you are going to install it in the trunk of a T roadster, I would think that you have room in there for a somewhat larger battery if you choose to. I would get an AGM battery as they are more reliable and more able to recover when depleted. Smart chargers for them are small as well as inexpensive and could be carried in the trunk as well. Personally I would want more CCAs for those times when a problem does arise. How much more space does a decent size battery take? I realize that some cars really have a space limitation, but if a car has a trunk it seems that should allow more flexibility in your choice.
Go to the parts store and see whats most popular. Any modern V6 motor and up will have enough cranking for your needs.
I had a Braille (SP?) battery installed up over the pass rear fender well of my 31 Model A as it was small and didn't take up much space and could be mounted in a variety of positions. I used a battery tender on it when not in use but it didn't last 2 years. I replaced it with a conventional car battery with as many cold cranking amps as was reasonable. This car only has the basics such as lights, horn, and so on... I just decided to give up that little extra space to be sure the car would start.
I use group 34s in everything, can get them with 1000 cranking amps. Even in the dead of winter they'll crank up big blocks. They are an inch shorter than 24s. Common enough that the local wrecking yard usually has 2 or 3 at a time for 35 bucks a piece (yeah I'm a cheap bastard)
I’m rebuilding my 54 F-100. It will have a SBC. I decided to go with a group 48 because it is used in most GM cars over the last 10 years or so, so I can get one anywhere.
You Betchum Red Ryder, that is exactly and only what it means. Post orientation is set up to work best with a Ford. Put a regular 24 in that same Ford and the cables often don't reach or the posts are too close to something you don't want them close to like the hood on some cars. Same with putting the 24 F or any F in a GM car or truck, It is a strain to get cables to reach. I just pulled my couple of years old battery out of my 77 C30 and stuck it in my mom's 76 F250 and ran into that. I just decided that If I was spending 200 bucks on a new battery the new one was going in my truck . One thing, back to the original question, The group 24 or 24F can be found just about everywhere and usually places sell the "good one" with a higher cold cranking amp rating. That goes back to Rusty Rocket's original question "easy to find everywhere". Those little red batteries are cute but are you going find one in Podunk junction on Sunday afternoon on the way back from a rod trot with 3oo miles to go to get home? Someone is going to have a group 24 or 24F be it Costco, Walmart or O'Reilly's, Autozone or Napa. I buy my batteries and tires from the Les Schwab tire store chain here in town because in the PNW I am never far from one of their stores. They may or may not be better than what other places have but if something craps out on the road battery or tire wise I can usually get it fixed and go. One store even let me use a loner tire when I hit a chunk of scrap iron in the road and ruined a new tire and ordered a new replacement to be delivered to my home store for the car, The loaner went on the truck back to the dealer that let me use it to go back with the set of takeoffs they had.
Nice to learn something on the 24f, thought it had to do with top orientation like with the 24t and the threaded post. I had heard there was also a subgroup 24h?
I have a Dyna-Batt in my roadster, built a firewall behind the seat and hung it on the back, in the trunk - weighs 13 pounds and is ultra-small. https://www.jalopyjournal.com/forum/attachments/pxl_20230704_180015336-jpg.5775946/
High priced, but an 11 year warranty, and the jump start feature is pretty interesting. https://dakotalithium.com/product/dakota-lithium-lto-automotive-cranking-battery/
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