Car battery question

What you might be forgetting is that the figure of 725 CCA is simply the maximum that the battery is capable of delivering for 30 seconds at 0 degrees F. It is not the current required to start the car, except under extreme circumstances. In very cold conditions, the batteries performance can drop by as much as

25% of the CCA figure. Add to that, that the battery may not be fully charged, and that it's performance degrades over time anyway, it will be obvious that the battery should exceed the maximum that might be required of it for most of it's working life. Or at least until the guarantee expires. :-) I don't know what engine requires a CCA of 725. I have a heavy duty 70 amp/hour battery fitted to my Rover SD1 V8. It has a CCA of 570, which is greater than that recommended, but I think you'll find most OE car batteries will have a CCA much less than this figure. A CCA of 380 rings a bell. I still reckon that for the majority of the year, most starters even first thing in the morning will take less than 300 amps to start the engine. Mike.

Land Rover Turbo Diesel. Just over 800Amps at 8.5V needed to start it.

As I indicated in my post, I'm sure that the 800 amps is the battery rating, not the actual current that the starter motor needs. I'd guess that normally it wouldn't be taking more than about 400 amps. Mike.

Yes and I read your post. At peak on starting it pulled 800Amps. Once the battery dropped 1V below spec it wouldn't start without a jump. Given the price of batterys that size it was cheaper to replace the starter with one out of a TDI that the clamp meter showed pulling a measly 550Amps.