Invisible wrote:
> 
> Well, it does say "ages 5 and above"...

As assumed :).

>>> Yeah. That's because there's a limit to how much current the battery can
>>> supply.
>>
>> And that's because of the internal resistance. If there were no such
>> thing, what would limit the current?
> 
> I'm sure there's a logic there somewhere - it just doesn't make any
> sense to *me*. ;-)

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.

>> Actually cars use lead acid batteries because they still are just the
>> best way to deliver that current reliably. NiCD -batteries can't stand
>> uneven charging, NiMH -batteries can't deliver enough current IIRC,
>> Litium batteries (both LiPo and Li-ion) can't stand water-freezing
>> temperatures. It all actually makes sense :).
> 
> ...as I said, you need the wattage to turn the starter motor. ;-) 

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.

> 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.

BTW, when there's *really* cold outside, the battery won't give as much
current out, thus not starting the car. To beat this you can use the
internal resistance to heat up the battery a bit (eg. by putting your
park lights on) and then start the car. Viva la resistance!

> Not if you expect the headlights to work while the engine isn't running.
> ;-)

True. The headlights are traditionalle 55W halogens and tail light
(which are lit when headlights are lit) 5W halogens (and there's usually
4 of them). Parks are also usually 5W halogens, that makes
55*2+5*6=140W, which makes ~12A of current, which makes under 6 hours to
drain the normal ~60Ah battery empty or less to drain it to the point
the current won't be enough for starting the engine. Therefore it's a
good idea not to use the headlights too much while the engine ain't
running ;-).

-Aero

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