Battery Acid for our particular batteries would be Sulphuirc Acid, 1 to 15 ratio to De-ionised water/distilled water.
I use a 80% sulphuric acid and can be readily obtained in 500ml bottles in Europe with out to many issues. So 500ml would make about 7.5 litres, (about 1.5 us gallons). ..... See pic of bottle in my Fume cabinet, with the label disappearing from just the fumes alone.
I think that this homemade battery topic may be raising false hopes regards getting batteries cheap, and now its getting technical and in the Dangerous Acid discussion area. Perhaps another more technical Forum may be better appointed. Depends on the Mods here?
Safety protection at all times.
PLEASE PLEASE remember, NEVER NEVER NEVER ADD water to the NEAT Sulphuric ACID solution.
ADD the Sulphiric Acid to the water very carefully and slowly, and let it disperse within the water. Even so when adding correctly in just one go, in one spot on the water, the solution gets very hot very quick, and spits and spatters.
Don't mess with neat sulphuric acid it does permanent damage to our fleshy bodies.
Everything is possible, just give me Time.
The OzInverter man. Normandy France.
3off Hugh P's 3.7m dia wind turbines, (9 years running). ... 5kW PV on 3 Trackers, (5 years) .... 9kW PV AC coupled using Used/second hand GTI's, on my OzInverter created Grid, and back charging with the AC Coupling and OzInverter to my 48v 1300ah batteries.