This is the 4555th most frequent Turkish word.
batar
"Sink" or "it sinks."
Here, 'batarsın' conveys the action of sinking into a swamp, emphasizing a literal meaning of the word.
Bu bataklığın içine girersen batarsın.
If you enter this swamp, you will sink.
In this sentence, 'battı' is used metaphorically to indicate falling into debt or financial problems.
Adam yanlış bir yatırım yaptı ve işleri ters gidince borç batağına battı.
The man made a wrong investment and when things went wrong, he sank into a swamp of debt.
The word 'batar' here relates to the natural phenomenon of the sun 'setting' below the horizon.