Cold Cranking Amps

[Mad Mac]

I need a new 6 volt battery. How many CCA for the Model A?

[MikeK]

Henry's original battery was about 175 cca although batteries were not rated that way back then. A typical bottom end group one 6v used by lots of 'A' guys will be 500 to 675 cca depending on build. The A starter draws less than 160 amps while cranking. Stalled it can draw upwards of 225 amps.

[Mad Mac]

Thanks MikeK, for your useful reply
I have had a deep cycle 6-volt battery in my Model A for 9 years and it has performed very well, but has now finally died. I am not asking about the pros and cons of deep cycle batteries, as they are the only type available here at reasonable cost ($NZ185).
What I do want to know is the relationship between cold cranking amps (CCA) and amp hours (AH). That is because the suppliers of deep-cycle batteries here in NZ no longer quote their Cold Cranking Amps, only their Amp-Hours. So my question is this: How many amp-hours should I be looking for if I want 600 Cold cranking amps?

[Kurt in NJ]

pick the largest one that fits in the battery box having reasonable terminal location
A car(starting battery)is made to give a lot of amps for a short time
a deep cycle battery is made to give low amps for a long time, this is why they don't have a cca rating
A used golf cart battery (one that wouldn't do 36 holes) worked in my smiths compressor for several years, I have also removed the excess voltage with a sawsall from late model mercedes agm battery, after 6-8 years the computers don't like them, but in a "stupid" car they go another 4-5 years

[MikeK]

The relationship between starting and deep cycle batteries in general is based on a few key differences:

1) Ratio of available electrolite sulfate ions to plate surface area-
True deep cycle batteries have a lower peak S.G. when charged and a larger volume of electrolite (more total sulfate ions). This permits a more even discharge amperage profile and longer life when cycled repeatedly from 100% down to 20% and back.

2) Physical construction-
Starting batteries pack more plate area, with thinner, thus closer plate separators into a given case size. They generally use the traditional 1.265 S.G. 36% H2SO4 electrolite, often with 'enhancers' in builds with Lead/Calcium plate alloys. More whalop (CCA) at the top 25% then they start on a sloping nosedive. The bottom 30% or so will have lower open circuit voltage and higher internal discharge resistance.

There is no magic linear multiplier formula for converting CCA, Amp Hours, and Reserve Capacity between each other. It is a logarithmic function for each factor in a specific build, thus virtually impossible to compare between different sizes and manufacturers.

The general trend in build differences between Starting vs.'Deep Cycle' lead plate/H2SO4 batteries is actually based on case size. Those in the traditional automotive case sizes, with automotive type terminal lugs do not take the differences to the extreme. They will do fine in cars without diesel or high compression V8's. You may only get 10 cranks at zero Fahrenheit (-17.8C) vs a dozen or more with a 'starting' battery, but if you can't start in half a dozen cranks you have other issues.

Those built in cases for golf carts, fork lifts, solar and wind storage, etc. take the construction differences farther. They do not do well in near short-circuit applications (CCA) but they do excel in reserve capacity. A short circuit test (CCA), like done on automotive batteries with a carbon pile tester, may permanently damage them. They also have open capped cells and require periodic maintenance of both water and electrolyte specific gravity between cells.

All that said (for the 2% that are still reading), original old car batteries, those with the tar sealed cells in rubber cases like the original A batteries, were ALL what we would now classify as 'Deep Cycle', not starting batteries. Automobile manufacturers simply put in what met the cranking demand, not 3X as much.

Why anyone would need 500 or 600 CCA for a vehicle that will never demand anything approaching 200 is perhaps based more on he-said, she-said testimonials than the truth. 'Bigger is Better' works for fork-lift and tractor counter weights but not so much for vehicle batteries.

[Mad Mac]

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Thanks again MikeK,
As one of the 2% I appreciate your comprehensive answer. Disappointing to hear that there is no standardised multiplying formula to make life more simple for an old guy like me, who doesn't know the first thing about electricity. I will just have to buy one and see if it works. I imagine it will, as the existing deep-cycle battery has performed well in my '29 RPU for the last nine years.