Author Options:

How many amps does a car battery have not cranking? Answered




8 years ago

Technically speaking, if the auto is turned off, perhaps a few millamps to provide power for any inboard clock, blinky leds to pretend the car is secured, etc.

(Amps are flowing current, not capacity for flow)

The capacity varies by battery model and type, but several hundred is a rough approximation, although it's limited by time of use and voltage droop.


Answer 8 years ago

I don't think car batteries HAVE much storage anymore - I doubt ours is more than 50-60Ah, the CCA is several hundred though....just not for very long....



Answer 8 years ago

Perhaps not. I was going on memory, from the days where I had a beefy die-hard in my SUV (which I recall had cold crank of about 100 Amps). I drive a dinky little Honda now and have no idea what's inside it. Perhaps, like you,  a 60A cold crank.

Still, I also remember from my days supporting battery powered experiments for uG research,  that most batteries can be stressed into delivering far more output. As you said, just not for very long (first, due to the finite capacity of the cell group, but also accumulated stress to the unit via overtaxing its output). I routinely took SLA cells that were rated @ 5AHr and pulled 30-40A from them. In one case, I used them to deliver 100A to ignite a ~13mm x 40mm compressed pellet of a mixture of metals (aluminum, tungsten, and a couple other tertiaries)...They were Hawker X-Cells (now Brit owned I believe under a new company name)  a slightly larger format than the familiar "D" cell.

Hence the nature of my comment, since auto batteries are far beefier than a little X-Cell. I wouldn't recommend doing it all the time, since it will kill the battery in short order. That's why manufacturers rate them in cold crank Amps. Maybe not what they're actually capable of, but what they're capable of and still maintain the warranty...


Answer 8 years ago

Most car batteries now are between about 50AH (for dinky little cars) to about 100AH for things like larger diesels (which need more oomph to start).

This however is the AH - and providing the power is taken out at a reasonable rate (eg: over 10 -20 hours), this is about what you would expect to get if the battery was in new condition and fully charged.

In other words, if you bung a 60w car bulb (nominal draw 5A), then an 80AH battery will keep it burning happily enough for about 16 hours.

Cold Cranking Amps are a different beast altogether - and measure the ability of the battery (even when partly discharged) to supply a specified current for thirty seconds for the starter motor when cold - 18C or 0F - and the voltage must not drop below 7.5V during the 30 seconds.

A starter motor on a 2 litre diesel in the middle of winter will probably take about 5KW - which if we can be naughty and call it 4.8Kw to make calculation easy), means we will be pulling around 400-500Amps (remember nothing is 100% efficient especially cheaply made motors).

So if you had a REALLY well built NiCad battery (of the type used in model aircraft) where even a C-cell can provide current of around 140A (no typo) - with almost zero volts drop (unlike the car battery), then you could end up with a battery having perhaps 50 cells in a 10x5 series / parallel arrangement which would give you perhaps as little as 700A Cold Cranking but with only 15AH

Very rough and ready summary:

Modern (UK) Petrol Car battery 50-80AH - Typically about 65AH / CCA 400
Modern (UK) Diesel Car battery 70-120AH - Typically about 90AH / CCA 700

AH tends to be used more for deep discharge batteries however and car batteries are tending more towards the RC (Reserve Capacity) the RC is the amount of TIME the fully charged battery can supply 25A (at 80 degrees F) before the voltage falls to 10.5V.

Hope that helps.