Battery Size

[Bdhand]

My parts person is asking me what group size the battery is for my 1966 bronco 24, 26 or 35 and what size cold cranking amps. Any body got a clue.

 

[904Bronco]

Group 24 is what I bought, Group 27 was optional in many years.
Use the demensions of the 24, then look for the similar sizes that offer the most CCA.

Next would be terminal position, there is 24F and plain 24. 24 has the posts towards the firewall with the negative closest to the fender and positive closer to the center of the motor. 24F is the opposite, posts switched.

 

[hammer189]

If you intend to swap post locations (to get the + away from the metal fender) make sure the wires are long enough. If the wires are long enough I would swap the post locations. Little piece of mind. David

 

[DirtDonk]

General rule-of-thumb for choosing cold-cranking amps is to double the engine cubic-inches. So for a 302 anything over 600cca is considered acceptable. But as said, the more the better in most cases.

But at 600 you have more than enough for standard usage. As important, if not more for a utility vehicle that gets used for many different things would be reserve capacity (RA) and here again, the more the merrier.
These days it's pretty easy to get an RA of 120 which is 120 minutes of use at a specific draw (I think it's 15a or so?) and gives an indication of how long you can use the battery with the engine off before it can't start the engine.

If your battery cables don't reach with the new configuration, then it's a good excuse to up-size the battery cables to 2ga as well. Cheap insurance...

Overkill is just enough.

Paul

 

[blubuckaroo]

I've got to disagree with the old school battery requirements.
If you've swapped your big ol starter for one of the newer smaller permanent magnet starters, you're battery and battery cable can be much smaller too;.

 

[DirtDonk]

It's not a requirement. Just a good sensible recommendation. Even with the old original style starters Ford only used 6ga cables. Worked plenty well for the basic stuff. For me it's all about "future-proofing" things.
In the future, what if a cable is damaged or compromised with corrosion? A larger one will carry more current longer.
What about a failing starter that's pulling too much current? A larger cable can handle it and a larger battery has more reserve to get it cranking.
What about four-wheeling when you use your starter to literally push your vehicle up and over an obstacle while you're dancing on the clutch and gas and brake pedals with only two feet? Larger cables and a more powerful battery will get you easily over this hump.
What about a really cold morning when the battery is no longer brand new, but perhaps is five, seven, or even nine years old (if you have a good battery)? The low crank-a-bility of the tired battery working extra hard to turn over an extra cold engine with extra thick oil in it will end up much better for the owner when the battery has extra capacity left it it's repertoire and the cables can handle the added current.
And when you up-size your auxiliary body ground cable commensurate with the larger main cable, when the main cable fails, or comes loose (as they often do) then instead of literally melting your throttle cable or rod, or any other connections as the starter current hunts for a good ground, your now super large body ground might just be enough to take the load off of all the rest of the stuff and get you home again. Even if it does not crank right away, at least the current has a path to go without taking out the metal bits in the area.

Probably other good reasons for making sure your battery cables are over-sized and your battery is ready to give you extra duty when it's really, really needed. But I'm convinced it's a good idea.
Nothing wrong with staying stock if that's what you want. Lots of people do it. But many more benefited, or could have benefited, from up-rating your battery and cables.

Paul

 

[anoblefox]

I concur with dirt donk, I always measure the battery box and install the largest physically sized battery that will fit, in all of our vehicles. YMMV

 

[B.ranch]

I have had good luck with optima batteries, 3478 red top is in my bronco, it's has performed very well

 

[rguest3]

I use the Odyssey 34/78. Plenty of power even for a modified truck and has top and side terminals.

 

[blubuckaroo]

It's not a requirement. Just a good sensible recommendation. Even with the old original style starters Ford only used 6ga cables. Worked plenty well for the basic stuff. For me it's all about "future-proofing" things.
In the future, what if a cable is damaged or compromised with corrosion? A larger one will carry more current longer.
What about a failing starter that's pulling too much current? A larger cable can handle it and a larger battery has more reserve to get it cranking.
What about four-wheeling when you use your starter to literally push your vehicle up and over an obstacle while you're dancing on the clutch and gas and brake pedals with only two feet? Larger cables and a more powerful battery will get you easily over this hump.
What about a really cold morning when the battery is no longer brand new, but perhaps is five, seven, or even nine years old (if you have a good battery)? The low crank-a-bility of the tired battery working extra hard to turn over an extra cold engine with extra thick oil in it will end up much better for the owner when the battery has extra capacity left it it's repertoire and the cables can handle the added current.
And when you up-size your auxiliary body ground cable commensurate with the larger main cable, when the main cable fails, or comes loose (as they often do) then instead of literally melting your throttle cable or rod, or any other connections as the starter current hunts for a good ground, your now super large body ground might just be enough to take the load off of all the rest of the stuff and get you home again. Even if it does not crank right away, at least the current has a path to go without taking out the metal bits in the area.

Probably other good reasons for making sure your battery cables are over-sized and your battery is ready to give you extra duty when it's really, really needed. But I'm convinced it's a good idea.
Nothing wrong with staying stock if that's what you want. Lots of people do it. But many more benefited, or could have benefited, from up-rating your battery and cables.

Paul

So, if you've swapped in one of the new permanent magnet starters, you would still increase the size of the battery cables? That make no sense to me.

 

[bronconut73]

So, if you've swapped in one of the new permanent magnet starters, you would still increase the size of the battery cables? That make no sense to me.

Oh Blu....

You know we like overkill.

I'm running the fattest battery cables I could get at the wire supply wholesaler in town. I made a custom battery mount and use a group 31 Optima. I have the marine solenoid and yes, the pmgr starter. Oh and I have a second Optima on the other side of the engine compartment where my windshield washer used to be.
This extra battery can piggy back my starter battery if I need a jump or isolated for use just for the winch.

Overkill?
Hell yea.
'Mericuh.

 

[blubuckaroo]

Oh Blu....

You know we like overkill.

I'm running the fattest battery cables I could get at the wire supply wholesaler in town. I made a custom battery mount and use a group 31 Optima. I have the marine solenoid and yes, the pmgr starter. Oh and I have a second Optima on the other side of the engine compartment where my windshield washer used to be.
This extra battery can piggy back my starter battery if I need a jump or isolated for use just for the winch.

Overkill?
Hell yea.
'Mericuh.

It's called "bragging rights."

 

[bronconut73]

It's called "bragging rights."

It is that too.

 

[johnbeck]

Today I just installed a 34/78 battery and new cables. I like having the side mount connections for accessories. My solenoid is older, I chatted with Paul some time ago and he had told me of some quality solenoids - one being a marine one. Paul, Bronconut 73, do you guys have part numbers handy? If not I'll dig through the archives. My wife has been ill for eight months and I'm finally getting some time to work on the Bronco. Thanks, John B.

 

[DirtDonk]

Sorry to hear about your wife John. I don't have the number handy, but will see if I can put my hands on the part to get it.

Paul

 

[Broncobowsher]

I go with the heaviest battery that will fit the hole. Weight = lead = capacity

 

[bronconut73]

Sorry to hear about your wife John. I don't have the number handy, but will see if I can put my hands on the part to get it.

Paul

I got the part number here on CB but don't remember it.
I ended up at a boat supply website.
The solenoid was brown.

 

[johnbeck]

I installed 4 gauge wiring, will go back with 2 gauge to the starter in the future. I'm curious, is my standard Echlin solenoid limited in it's amp carrying ability - is it a weak link in the circuit if I run 2 gauge in to it and 2 gauge out? It probably would take a series of long cranks to melt it down, right? Thanks, John B

 

[Madgyver]

I used an Interstate battery from Costco. A little bigger than the stock battery tray but I can modify that.

 

[Seventee]

I used an Interstate battery from Costco. A little bigger than the stock battery tray but I can modify that.

That's the same exact battery I have. Been great for 7 years! I don't remember having to modify the battery tray.