Lead acid battery question.

[Larry Edgerton]

I have been trying to find an answer to this question on the net but have not come up with the proper search, so.......

If I have two identical size car batteries, one with say 650 cold cranking amps, and another with 1300 cold cranking amps, what are the physical differences inside the battery that make it have more cranking amps in one when they are the same outside dimensions?

Thanks, Larry

[roger wiegand]

Number of plates-- the amount of surface area of lead available to react. A high CCA battery will have more, thinner plates.

[Larry Edgerton]

I thought it was the number of plates that established the voltage, six sections at roughly two volts each?

[Dan Hunkele]

1300 CCA battery will be markedly heavier.

[Jerome Stanek]

I thought it was the number of plates that established the voltage, six sections at roughly two volts each?

It's not the number of sections but the number of plates in each section.

[Lee Reep]

I thought it was the number of plates that established the voltage, six sections at roughly two volts each?
If more plates were wired in series, then you would get more voltage. (Think stacking batteries, i.e. two 1.5V batteries in a flashlight gives you 3 volts total.) Putting additional plates in parallel gives you more current at the same voltage.

[roger wiegand]

You can have different numbers of plates within each cell, there will be six cells in a 12V battery. The potential difference is not a function of the area of the plates--voltage (think pressure) is a function of the lead/lead sulfate electrochemistry, and is the same no matter the size of the cell, amperage (think volume) is a function of how big the pipe is, e.g. the amount of lead/sulfuric acid interaction area within a cell. Cells are connected in series to create a battery with a voltage that equals the sum of the voltages of each cell.

As plates become thinner and more closely spaced there is more danger they will warp and short out a cell. Deep cycle batteries have fewer, thicker plates, farther apart, for example to allow them to take many cycles of extreme charge/discharge and typically have lower amp ratings. Car batteries normally have much shallower cycles, so can be built with thinner, more closely spaced plates to deliver more amps.

308437

[Rod Sheridan]

I thought it was the number of plates that established the voltage, six sections at roughly two volts each?

No, the number of plates establishes the capacity, the voltage per cell is nominally 2 volts regardless of the size.

Obviously a car battery has 6 cells for 12 volts.........Rod.