Green’s Dictionary of Slang

batner n.

also battener, battner
[16C SE batten, for an animal to put on weight]

an ox.

[UK]Head Canting Academy (2nd edn) 170: Batner An Oxe.
[UK]B.E. Dict. Canting Crew.
[UK]B.M. Carew Life and Adventures.
[UK]Grose Classical Dict. of the Vulgar Tongue n.p.: Battner. An ox: beef being apt to batten or fatten those that eat it. The cove has hushed the battner; i.e. has killed the ox.
[UK]Lex. Balatronicum.
[UK]Egan Grose’s Classical Dict. of the Vulgar Tongue.
[UK]G. Kent Modern Flash Dict. 5: Battner, an ox.
[UK]Flash Dict. in Sinks of London Laid Open.
[UK]Duncombe New and Improved Flash Dict.