Green’s Dictionary of Slang

batter n.1

[SE batter, a form of paste]

1. [early 19C+] flattery.

2. [late 19C] (US) money [pun on SE batter/dough n. (1)].

3. [1940s+] (also baby batter) semen.

In phrases

belt one’s batter (v.) [belt v. (1)]

1. [1900s–40s] to copulate with a woman.

2. [1980s] to masturbate.

splatter one’s batter (v.)

[1990s+] to ejaculate.