Battery CCA/amp hours formula

John try this

Amp/hour = CCA / 6

I havn't checked this. so good luck

Hi,

I may be wrong on this, so if I am please feel free to let me know, as I don't claim to be any sort of battery expert, but it's my belief that no such 'formula' exists.

The reason is that you can have a battery with great CCA rating but very low amp/hour optimised for turning a motor over - ie producing a very high current for a short period of time, and on the other hand you can have a deep cycle battery with poor CCA rating optimised to run accessories such as fridges and maintaining a relatively low current flow, but steady voltage over a log period of time. So based on this theory, if one value rises, then the other value would not necessarily rise, in fact in many cases it will go down! The way in which these batteries are optimised for different roles is in their construction - from memory, the deep cycle will have a greater number of plates, and these plates will be at least 4mm thick - thereby making a larger surface area available for chemical reaction to produce voltage.

These batteries may both be very high quality batteries costing alot of money, but are optimised for different things, this is why you might see many dual battery setups fitted with a good starting battery (high CCA number) for starting the vehicle, and a deep cycle auxilliary battery for running low current accessories over a long period of time.

Two examples:

Yuasa 68MF has 525CCA, and storage capacity of 68Ah

Optima D34 has 870CCA, and a storage capacity of 55Ah

(Thanks to 4WD Monthly for those stats found on page 130 of the Aug2003 edition)

The Yuasa has a larger storage capacity than the Optima, at the cost of it's cold cranking power whilst the Optima has excellent cold cranking ability at the cost of it's storage capacity.

Another example (also from 4WD Monthly) is:

CGB CB12100 which has a massive 900 CCA cold cranking amps, and a big 100Ah storage capacity.....

Yep, batteries are a science :-)

Cheers,

Luke.

Fromm an earlier post in which I took an interest:

"Mark, Dug this formula up using Google [wanted to know myself seeing you asked] Cam from a University of Hawaii electronics website. hope it is of use: Many batteries today are rated in CCA or RC. CCA is Cold Cranking Amps. CCA is approximately equal to the RC of a battery times five. [1000 CCA is about 190 RC]. RC is Reserve Capacity. You can convert RC to amp/hours by the following formula: Amp/Hours = (Reserve Capacity / 2) plus 16"

John have a good old look in the archives here you will find the formula , an overlander 700 / has a cca 600 / rca 130 / is actualy rated at 68 amp hrs /the ducks guts for the info is the university of Hawaii web site.

John.

There is no relationship between cca and ah. the type of construction is the only determinate of these two parameters. the cca is limited by internal resistance of the cells not the capacity. Eric.

Interesting thread indeed!

It seems, as I first thought that the general consensus is that there is no direct relationship between CCA and AH, and that those merits are dependant on battery construction techniques.

This is certainly the idea that I've always been familiar with....

Maybe someone from the University of Hawaii will come over and explain their "Formula".

Cheers,

Luke.

:-)

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