Green’s Dictionary of Slang

1. (US milit.) coffee.

1941		S.F. Chronicle 1 June H5/7: The draftees assigned to Camp Claiborne, in Louisiana, got out a glossary of slang terms to describe everyday things in army life [...] The Louisiana lads call [...] coffee, ‘battery acid’.
1944		H.B. Hersey G.I. Laughs 171: battery acid, coffee.
1971		T. Thackrey Thief 191: There was still some battery acid left [...] I dumped a little of it into a pot and put that on the stove.
1975		L. Dills CB Slanguage 7: Battery Acid: truck stop coffee.

2. (US milit.) synthetic lemon juice.

1946

J.W. Bishop ‘Amer. Army Speech’ in AS XXI:4 Dec. 244: Powdered synthetic lemon juice, alleged to contain vitamin C and very prevalent in K rations, which I have sometimes heard called ‘battery acid’ and ‘bug juice.’.

3. (drugs) LSD [play on acid n.¹ (1)].

2001

ONDCP Street Terms 2: Battery acid — LSD.

4. (Aus.) a bottle of cola.

2016

N. Cummins Adventures of the Honey Badger [ebook] The orders [...] usually consisted of a rat coffin or a leper in a sleeping bag (sausage rolls), maggot bag, dog’s eye or mystery bag (pies), dead horse (tomato sauce) and battery acid (cola).