Something did not compute thanks.

I suppose its possible its not pure, but for two bucks for almost
two liters I couldn't refuse. I'll be trying it on test strips first.

The concentration is more to my liking than reagent grade
meerly do to the handling issues.

I'll be calling B&H for control strips tommorrow (which is a special order)
any where you know of the might stock actually them?

Reagent grade surely is standard -- but use of concentrated acid, rather
than a standard dilution, isn't necessarily standard (especially with
acids like nitric, hydrochloric, and sulfuric, which are relatively
hazardous to handle in concentrated form).  I've seen many formulae (not
necessarily only photographic) various places that called for a standard
dilution of this or that, either because it was more available, less
expensive (even after figuring how much was just water), more convenient
to measure, or simply because it was significantly safer to handle.  I
would surely place sulfuric acid in the last category, even if none of
the former.

For bleach, where the formula calls for (IIRC) 10 ml of acid in a liter
of working solution (for which I'd substitute about 28 ml of the 35%
battery acid -- have to do the math with a calculator to get the exact
figure), the only good reason to use reagent grade is, as you suggest,
to avoid unknown impurities.  Given the differences in both price and
handling (I can buy a liter size pouch of battery electrolyte for a lot
less than the hazmat fee on the shipping of a minimum quantity of
reagent grade acid, and it comes packed in a shatterproof elastomer
pouch instead of a glass jug), I'd consider it worthwhile to try the
battery acid.  It's cheap enough to simply dispose of if it turns out
not to work well, and if it does work well, it makes a huge difference
for my use (and probably for Greg's, as well).

That's the way battery acid is normally distributed; acid recovered from
recycled batteries is disposed of as hazarous waste.  It's not the lead;
that's relatively easy to precipitate any remaining lead that might be
in solution (neutralize with baking soda or chalk, and the lead sulfate
will precipitate).  It's cadmium, which stays in solution better than
lead (cadmium sulfate is about as soluble as silver sulfate, and will
remain dissolved at hazarous levels in a neutral solution), and is added
to the plates in modern batteries to extend their life.

Last time I had battery acid around, it came to me in a small rubbery
pouch (I think it was some kind of silicone elastomer, in fact) that was
to be used in filling the (dry charged) battery immediately before
installation or in the store for rack charging prior to sale.  Battery
acid obtained in containers, rather than manually drained from a battery
by the end user, should be plain technical grade acid diluted with
filtered water to working strength (the water is filtered in a manner
that specifically removes chlorides, most likely reverse osmosis;
chloride ion poisons the reaction that makes a lead-acid battery work).

Basic precaution in handling battery acid is to neutralize the working
area with baking soda after work is completed -- specifically to prevent
evaporative concentration warned of in another thread.  Also worthy of
note, a tiny drop of battery acid will eat a hole in any cotton cloth
that won't show up until the article is laundered and the damaged area
crumbles or dissolves in the wash water.  It's similarly hazardous to
eyes; wear goggles (or, better, a full face shield) as well as the heavy
neoprene or nitrile gloves, and preferably a neoprene coated apron as
well.  Have an eye wash available (a shower works very well for this),
and keep a box of baking soda handy.

You need to check if it is 35%, or if it is diluted down for filling
as is. 35% is diluted before it is used in the batteries, but nowdays
they may well be shipping the more dilute read to use conc so as to
not confuse the burger flippers.