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.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
batch * batchelor’s fareNathan Bailey's 1721 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes