[Shop-talk] Battery Fluid

[Peter J. Thomas]

On 6/23/2012 10:01 AM, Bob Spidell wrote:
> On a recent road trip (4K miles in 10 days) in my Austin-Healey 3000 I 
> had a battery spillover problem.  I first noticed my arm would itch 
> after I went to retrieve something from the boot (trunk), then saw 
> some fluid near the battery.  When I got home I pulled 
> everything--including the gas tank--out of the boot and flushed with 
> baking soda solution to neutralize the acid.  I discovered the voltage 
> regulator was overcharging and replaced it.  That problem solved.
>
> Since I'd lost actual battery fluid--concentrated sulfuric acid--I 
> bought some battery acid and topped-up the battery's cells.  This got 
> me to thinking; usually, you top up a battery with distilled water.  
> This is because, presumably, you're just replacing the water portion 
> of the acid that evaporates during normal charging and discharging.  
> I'm wondering if a) after topping-up with distilled water a few times 
> would it be a good idea to top up with acid, and b) would it be even 
> better to always top up with acid?
>
> I'm thinking maybe yes to "a," but probably no to "b," since I know 
> from my days as a chemistry student that acid strength depends on a 
> proper mixture of water and the acid agent (in this case sulfur 
> trioxide).
>
> Thoughts?
>
> Bob
>

You could just check with a batter hydrometer.  It measures the specific 
gravity of the battery fluid and you would know if you need acid.

Peter T.