Eero Ahonen wrote:

> 
> That logic IS the internal resistance. You'd just need to put some mind
> to it (and maybe read a book for ages 15 and above), and you'd certainly
> figure it out.
> 

I was going to say something like the reaction rate inside the battery 
caps the amount of current the battery can supply, but I guess that 
would be under internal resistance.

> 
> Yes. You can have the wattage from numerous different battery types. The
> problem is that you can't have the wattage from any other battery type
> reliably enough, or in a package that actually fits in the car.
> 

Lead-acid works well in this application because it can tolerate only 
brief cycles. If you drain a lead acid battery completely, it won't 
recover well. But the advantage of that chemistry is the fast reaction 
rate, which allows the battery to supply a huge amount of amperage in a 
very short time. Other chemistries can tolerate deep cycling (near full 
discharge), but cannot tolerate the very small discharge/recharge cycles 
that are required in a car, e.g. NiMH and NiCd both tend to develop a 
"memory" (NiMH significantly less so, but it does happen) Other 
chemistries don't like being cycled frequently, and will wear down rapidly.

>> If you
>> only needed electricity for the sparks and lights and stuff, you
>> wouldn't need nearly as much power. (Freezing would still be an issue
>> tho...)
> 
> Yep, indeed it would. Lead acid handles freezing temperatures incredibly
> well and in small package.
> 
>

The alternator usually provides all of the current needed to run the 
accessories when the engine is on. This can be proven if you've ever had 
to jump an entirely dead battery and drive to the local auto shop to buy 
a replacement...

-- 
~Mike

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