Thread: High CCA but low Ah: why?

Hi bamberg and welcome to the forum.

As to your battery question.

The CCA rating of a battery is based on what it is designed for and not on the batteries actual size and there is actually no relationship between a battery’s CCA and it Ah.

As in your case, the battery has a high CCA but a small Ah.

Many conventional deep cycle batteries have the reverse. They can be 100+Ah but have a very low CCA, and most do not have a CCA rating at all, because they are not designed as starting batteries.

Hi

Odyssey PC1500 only has 850cca not 1500 or am i reading that wrong

In horse racing parlance, it's a sprinter, not a stayer. More Black Caviar than Makybe Diva.

Hope this helps.

CCA is the capacity of the battery to deliver current at a moment - the higher the CCA the more current it can deliver.

Amphour capacity is the capacity of the battery to deliver current over time.

As example, if the battery can deliver 1500 cranking amps it means you could put a 1500 Amp load on it and it would be OK whereas a 3000 Amp load may destroy it.

How long it can deliver that load depends on its aH capacity. If a battery is rated at 100Ah it could deliver 1 Amp for 100 hours or 100 Amps for 1 hour. In practice the figures don't quite work out but this gives you an idea.

In your case the battery can deliver 1500A but it would only be able to do it for about 2.72 minutes, i.e., (68*60)/1500 minutes. This is, of course, theoretical as it would get super hot and a continuous drain at that rate would NOT be recommended.

Now as to the question of its purpose. It is for starting the car. You need a deep cycle type battery to drive your ancilliary equipment as car starter batteries are not designed to recover from deep discharge, rather for a heavy load over a short period (starting).

You can get the best of both Worlds by using the SuperCharge Allrounder or some Century marine Batteries. These have the normal posts for connecting to your car electrical system but also have screw terminals for your ancilliaries.

However, if your ancilliaries are going to be placing significant demand on the battery such that it may run flat (e.g,. fridge while camping) you would be better of using a dual battery system.

Howard

Originally Posted by bamberg

An Odyssey PC1500 with cranking amps of 1500 seems like a mighty powerful battery but why is it only 68 Ah rating.
Also, is this battery for starting, for auxillary stuff, or both? I have a Defender Td5 (2005).

if you are puzzled that a battery could have a big figure for one measure and a small one for another, think of it as a bucket with a hole in it.

A big hole will let the water rush out quickly, a bit like having a high figure for CCA. If it is only a small bucket with a big hole, it will be empty very quickly, so not many Ah.

A big bucket with a small hole will keep dribbling water out for a long time, so a lot of Ah, but the rate at which the water comes out will be quite low, so low CCA.

Batteries are a bit more complicated than buckets with holes in them but perhaps that analogy shows why something that can deliver a rush of energy or water isn't necessarily going to be able to deliver it for a long time.

I have two Supercharge All Rounders in my Rangie (obviously one starts the engine, the other is an aux), great batteries designed to be good at both cranking and slow discharging, but not awesome at either.

60hrs running my ARB 78L fridge, I get out of my aux before becoming low enough to need recharge!

Cheers
Keithy

Hi again folks and sorry but there is a lot more to battery’s CCA rating.

CCA stands for Cold Cranking Amps and means just that.

The CCA of a battery is the amount of current the battery, at 0F ( -18C ) can supply for 30 seconds without the battery voltage dropping below 7.2 volts.

Ah stands for Ampere Hours and the Ah rating of a battery is theoretically the amount of amperes the battery can supply till it’s flat ( 10.5v ) with a 1 amp load applied to it at an ambient temperature of 75F ( 25C ).

So you can not simply apply a current load equal to a batteries CCA and let it run “flat”, because you would drop the battery’s voltage to 10.5v in a few seconds while cranking.

And as for the batteries construction,
it is the surface area of the plates that give a cranking/starting battery it's CCA whereas a deep cycle or high A/H battery will generally have thicker/heavier plates with less surface area for higher storage but lower CCA and a dual purpose is a compromise or combination of both. Which is why the weight of a battery is as relevant as the size.
At least that is my understanding of lead acid batteries.

Cheers,
Paul.