Thread: CCA or Ah for batteries

Or, buy Optima battery's, that'll do both happily

Originally Posted by pawl

Thanks, but no thanks drivesafe, I will pass on trying to understand that Peukert guys stuff, all it it did was give me a headache.

Now you know why I wasn't going to try.

Pawl, Sorry if I made your decision harder by my last post. I was going off the theory I learnt becoming an Electrical / Instrumentation tech, but I'm not an Auto Electrican. I had never heard of the Peukert effect, but after much reading it makes sense. It seems things are not so black and white after all, if anything it has complicated the thought process of selecting batteries for me. I think from now on a good rule of thumb personally will be to just select the biggest sized battery I can to fit in the space I need. Thanks for the lesson people.

Incidently, I had posted on my wife's PC, hence the Username "TJWA's Better Half". I did that twice today.

This is an excellent thread. I think it makes us think about the uses we put our batteries to. For my use (winch, fridge, inverter) it is necessary to have both a high CCA starter battery (wired to winch) and a high AH battery for the auxiliaries. I actually have an AGM in the back with an isolator switch for this very purpose. It delivers low current over a long period with negligable internal resistance. And like TJWA is saying, the biggest CCA battery in the front that will physically fit!
Thanks everyone, including TJWA, for your explanations.

Peukerts Exponent for the layman.

Think of it like your fuel tank...

on the window of a new car the manufacturer puts a sticker that says X L/100K
thats roughly equivalent to the AH rating


now if you jump in the car turn everything on plug in a heap of electricals and load it down then drive flat out like a rice boy in city traffic your going to get worse fuel economy, the same amount of fuel wont go very far. Thats putting a higher amp load on the battery.

But if we turn everything off, unload the car as much as possable and just beetle around the motor way at 80 Kph at night time without stopping or starting your fuel economy will be better and you will receive better economy that whats on the sticker. Thats the same as only putting a light amps load on a battery.


Think of CCA as the amount of horse power in an engine.

a 100 HP engine pushing a load that needs 50HP is going to do it a lot better than a 50HP engine will so the 100 HP engine will last longer.

same same for the CCA, of a battery a 700CCA battery pushing a 100amp load does a lot better job of it than a 350CCA.

I always understood it as buckets, the cranking battery as a open bucket filled with water and the deep cycle as a bucket filled with sponge and water.
Tip the open bucket (crank battery) and all the water (power) flow out in a big rush.
Tip the bucket with the sponge (deep cycle) and the water (power) flows out at a slower, steady pace and for much longer.
Even thou both buckets hold the same amount.