OK , the common belief is the bigger the battery ( amps ) the better !!!
I read some info that makes sense & from a reputable source if I remember correctly , that TOO big a battery will strain the alternator to keep it charged !!! So you need to correctly size the battery !!!
Some quick research is the suggested size is a 24f or 27f . I am still looking for info.........
What are your thoughts & what size do I need if I have a stock system with no a/c (yet) , but will be connecting a radio & 2 300 watts min. amps & 4 speakers & maybe a sub woofer !

 

Battery size does not affect the alternator. If a battery is fully charged, the alternator is only supplying whatever the vehicle is using.

Back when I sold auto parts, I was told that if two batteries had the same amp rating, then get the bigger one if it will fit. The larger case holds more electrolyte and will run a bit cooler.

 

Well before some of you guys holler & say nonsense , this is what I just found...........
What is the ratio of battery to alternator?

A normal ratio would be 2.5 to 1. For example, let's say we have a 7 inch diameter crank shaft pulley and a 2.75 inch alternator pulley. We would divide 7 inches by 2.75 which equals 2.54 to 1. If the engine was turning 1,000 RPM we would multiply 1,000 by 2.54 which would give us 2,540 alternator RPM. ha ,.......... I actually am just NOW reading this & it is very technical.............

" This may be verrrrrrrry interesting " - ( Laugh-In - Arte Johnson ) lol.................lol...

 

Fully charged is the key , if you run at night with lots of accessories , you will drain plenty of juice , so alternator will have to replace this because I assume voltage regulator will sense battery needs more juice...........etc , etc...
I believe I read this first about the alternator & battery sizing thing in a special edition of HotRod books............HotRod is good info I think..........
This is where marketing MAY come into play . Companies tell people they need bigger , more fancy items to make more money . Sell them what that do not need ,upscale , upsale , I believe.........

 

A highly discharged battery of any size will draw high current from alternator for some time. But that is how the system is supposed to work. Battery is sized for starting capability. Alternator is sized for current load when running.

Suggest group 24 or the other flavors of similar capacity. I use an 'H6' which is size size as '24', but with recessed terminals.

 

You can talk about cranking amps, or cold cranking amps, but don’t ignore reserve capacity either.
Not completely universal, but typically a larger battery would have more reserve capacity, or RC.
That is the amount of time (rated in minutes) that the battery can be used without being recharged before it goes below a certain point. I think the standard test rating is using a 10 amp draw, if I am not mistaken.

If you’re going to sit around, listening to that radio all day, more RC is better no matter what strain it might put on the alternator later.
But I agree with the others that have said that charging the battery still works the alternator. A good quality alternator, especially the more modern designs, should be able to handl any size battery you throw at it.
Just make sure the wire gauge sizes for both the charge wire and the battery cables are good as well.
This is where sometimes a little overkill is just enough.

In the old days choosing the cold cranking amps used to be that you picked one with double your cubic inches.
So if you had a 302 you got at least a 600 cold cranking amp battery. At 351 got a 700 cca battery, etc.
For reserve capacity I always considered 120 minutes a good one. Many of the higher CCA and higher cost batteries were in that 120 minute range.
I have a big one in my pickup now that I think it’s 200. And it is physically very big.
But I don’t worry about my old 100 amp 1G keeping up with it and living a long life.
I’ve always used the biggest battery that would fit in a battery tray. And most Ford battery trays for me were oversized for the group 24.
My Broncos always got group 27‘s. And while that may have been why my cheap $19 alternators always wore out their bearings early (they never stopped charging though) I ran the larger case alternators for many years trouble free even with the biggest batteries.

For me, the choices are fairly easy then.
On an around the town cruiser on the weekends can get a regular old 24 battery and no worries.
A weekend adventure truck/work truck that might see some heavy duty use or have to jump other vehicles to start, or might need battery juice for extended periods, always gets the biggest, strongest battery I can fit.
And that truck always gets the most powerful alternator that is reasonable to install.

 

Interesting thing about my experiences with all of my cars and trucks.
In over 50 years of personal vehicle ownership, I’ve never had an alternator stop charging.
Some lasted only a year or two, some have lasted decades, and are still in use. But the ones that needed replacing always started making noise when the bearings got old.
Never had one fail electrically.
Knock on wood and cross fingers!

 

Wow, I've had all electrical failures over 30 years. never bearings. Internal voltage regulator or diode bridge gets cooked. Heat failures. but I live in PHX.

 

Yikes, I bet that heat does take it's toll.
I used to replace the old 19 dollar (then 29 dollars!) cheapo rebuilds from Kragen about every year and a half, to no more than three years.
At those prices, even back then I figured I got my money's worth. They kept chugging away, but I would eventually get tired of the grinding and rattling. Pretty sure I never over-tightened the belts too.
After dual batteries, when I replaced my last small-case 1G, I figured the large-case 1G version would last longer because it (probably) had bigger bearings. Never checked to verify the bearing size, but if not then maybe the larger components dissipated the heat better?
Either way, never had any kind of a failure with either a large-case 1G OR any of the 3G's and 4G's I've run. Simple swaps in some cases, and worth it.

The 70a version on my '71 had a lot of years and maybe 50,000 miles on it, when I "loaned" it to a buddy so he could sell his buggy Bronco without the high-zoot Premier Power Welder alternator included. Still working as far as I know.
The 100a 1G is still running I think, but haven't actually "run" it for awhile. So just assuming for my part at the moment.
The 120a Explorer 4G's are all good too. So far...

Admittedly I don't cheap out as much as I used to. Tried to learn from experiences when I can.
But so far, bigger has been better!

Sorry for the slight hijack there RTT

Paul

 

I have had a 72 40a 1G alternator crap out while driving at night. My 302 sucked everything out of the battery till it just out of nowhere it quit running. 4 years earlier the alternator wiring harness burned up so I rebuilt it in my dorm room. A diesel mechanic student friend took the alternator to class where he replaced the burnt terminal and tested it. That alternator ran for almost 100,000 miles.

 

Thank-you all ........1TonBaseCamp your post was amazing & quite agreeable with what I have read ! My reason for the post was expressed better in your post.
I will add that I read yesterday that a battery cannot ruin an alternator , but an alternator can ruin a battery . Now I do not know if I agree with that , but it does seem to have some logic .
I wanted to bring attention to us all that there is more to buying a battery than just bigger is better. It seems the way you use it is , as 1ton said is very important & one thing I wanted to express . I wanted suggestions as what size to buy !!!
I bought a 640cca battery & reserve was not listed & I forgot to ask reserve capacity .
I started this message more than 2 hours ago & am now finishing , I say this because I checked voltage of my new battery when I got home & immediately put it on charger because it only had 12.56v. . This seems sufficient to me but my research says 12.6 or less it is too much discharge , thus causing some damage to battery . How much damage I do not know & I think it was a utuber that said this so they may not know !!!
Any way trickle charger has still not fully charged my NEW battery !!! It has been charging for 3 hours or more.......... ha.............

 

My brand new 7/23 battery had 12.6 v or so when I got it home . Trickle charger showed it was low & charged it for 4 - 6 hours or so . Then it has been fully charged according to charger for 3 days or more I check it now & it has 12.6 v 12.7 v .
Fully charged , new battery should have 14 v or 13 v at the least shouldn't it ???

 

no, 12.6 is mostly charged. Only get above 13 V when alternator is suppling current to battery.

 

Thank-You Mr. Smoky___Diesel ,

 

Interesting thread.
I have a '68 Ford F-100 with a 427/C6 and the 427 is now a 449.
I put in a yellow top Optima, size 35 (35 was in there when I got it) and wondered if that big momma would do better with a larger battery as the battery tray is large enough for one.
I tried to find solid info and opted for the 35 as I saw nothing other than "get more CA/CCA" and while the yellow top is less of both than the old Red Top, I stuck with a 35.
Should I have gone for a larger Yellow Top? It seems fine, but still second guessing my choice...