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Re: Topping-off a battery (low Audi content)

At 04:17 PM 8/12/97 -0400, you wrote:
>>So, I notice that the electrolyte level in the battery in my '93 90CS
>>is looking low (it no longer covers the plates).
>Is this the Audi OE battery?
>>Can I just fill'er up with distilled water, or do I need to use
>>electrolyte? If the latter, where to obtain?

Electrolyte (sulfuric acid) is not needed - EVER (unless the battery has
leaked electrolyte).  If your battery is leaking you have a major problem
and need a new battery just for starters.  Any spills should be washed with
water and then with baking soda solution and then water again.

>As long as you don't need to fill up too much, use distilled water.  
>Note of course that this is counterintuitive, which is why you shouldn't
>put too much in.  The liquid should be an electrolyte.  It's usually
>sulfuric acid.  (in fact if you really wanted you could go to the store
>and buy some; an auto parts store might have some that would be the
>right concentration)  Tap water usually has electrolytes in it, from
>phosphorus, chlorine, metals, etc.  Properly distilled water has no
>electrolytes in it, which means that when you add distilled water, you
>decrease the power of your battery (not voltage) so it's less effective,
>especially on cold days.  If you're just adding a little, don't worry. 
>If you add a lot, you might try an auto parts store to see if they have
>battery acid.

NoNoNoNoNoNoNoNoNoNo!!!!!  Use distilled water *ONLY*!!!  Then run the
engine a while to fully charge the battery.  Thus speaketh the chemist.  :-)

If the liquid level is *extremely* low, add the water while the engine is
running and let it run until the battery is fairly well charged.

The sulfuric acid is essential for the battery to go through its
charge/discharge cycle.  The concentration of sulfuric acid in a fully
charged battery is higher than when the battery is discharged.  Since
sulfuric acid is more dense than water this allows you to check the
condition of the charge by using a hygrometer to measure the specific
gravity of the batteery liquid.  The hygrometer float will float higher in a
fully charged battery.

As someone suggested, loss of battery fluid happens mainly in two ways.
Evaporation of the water (not the sulfuric acid!) and electrolysis of the
water during the charge cycle.  Water is decomposed into hydrogen and oxygen
in a two to one ratio,  Anyway, water is what is lost.  Therefore water is
needed to restore the "original" condition.

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