Green’s Dictionary of Slang

bats adj.

crazy, insane, eccentric.

1924		G. Henderson Keys to Crookdom 397: Bats. Crazy [...] To go bats (crazy).
1928		J. March Wild Party 22: My sweetie’s bats— But I love her!
1934		H. Miller Tropic of Cancer (1963) 101: That cute little prick who drives me bats about his rich cunt.
1941		K. Tennant Battlers 16: ‘She’s bats.’ The Stray tapped her forehead. ‘Looney, like farver was.’ She added hopefully: ‘Maybe she’s escaped from a ’sylum.’.
1957		‘Nino Culotta’ They’re a Weird Mob (1958) 190: ‘Bats,’ he said. ‘Nutty as a fruit cake,’ said Pat.
1969		‘Iceberg Slim’ Pimp 97: I’m not bats, but I got to try this track.
1978		P. Theroux Picture Palace 17: He gave me that sideways glance again: She’s bats.
2000		Guardian Travel 5 Feb. 4: ‘I must be bats,’ I thought.

In derivatives

batso (adj.) [-o sfx (5)]

(US) crazy, eccentric.

1978		Penthouse Apr. 128: Look, I’m totally batso [HDAS].
1985		M. McCray L.A. Payback 54: Ratso’s gone batso. He always was a sick son of a bitch, and now he’s totally gone.
1994		R. Boyll Price of Fear 167: Going batso, are we? [...] Wanna play tic-tac-toe? Darkman considered it. The pastime of schizophrenics, playing tic-tac-toe with oneself.
1996		Indep. 16 May n.p.: A Year with Swollen Appendices, his chronicle of 1995, complete with batso speculations (‘28th May. Woke at 4.30. Funny thing – in Ireland I rarely get an erection...’).
1999		Terraquest 🌐 As opposed to Robbins’ highly methodical approach to climbing, ‘Batso’ Harding, as he is known in the climbing world, had a more organic approach. On a Harding climb, difficulties were dealt with as they arose and never without the aid of a good deal of wine, guts and humor.
2006		A. Bottagaro Poet, Count & Peddler 365: Prayer has kept me from going batso.
2013		Ted Dekker Blessed Child 148: The Greek was going batso.