Isaac Marino Bavaresco wrote:
> It takes much less than half the charge of the battery to start the engine.
> Usually you can start the engine lots of times in a short period without
> time for recharging.

Yes, but if you have a car battery that has been measured at 52AH and
draw 45AH from it, it will probably not start the car. Back when I
designed battery chargers I did lots of measurements of battery
capacity. And as I said, rules of thumb. If you take 26AH out of a car
battery, don't expect it to start the car unless it's under a year or
two old.

> I think the capability to properly start an engine is more related to
> the internal resistance. While the battery is able to source the needed
> current (hundreds of Amperes) with an acceptable voltage drop (anybody
> wants to investigate?) it will be able to start the engine.
> 
> Suppose a 5s start-up: 5s * 800A / 3600s/h = 1.11Ah

Very good. I think there is no conflict in our theories. With your
numbers, a fresh battery and my rule of thumb, you could start the car
25 times before recharging. I believe that. But not 50 times. Those last
few AH in the battery will not start the car.

The internal resistance changes in a lead-acid battery depending on the
state of charge, temperature, and general condition of the battery.

Cheerful regards,

Bob
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