I keep seeing constructions like “bater mal” and “bater certo”, and couldn’t quite see why “bater” was being used. I asked and (after a brief kerfuffle with some brazilians who tried to tell me that it disn’t exist and made no sense) found out that it is an informal expression. Bater is the verb used for the beating of a heart or the ticking of a clock, and if it starts going wrong that’s bad, so if someone “bate mal” after – say – a blow to the head, he’s not quite himself. You can also “bater bem” (being in good form) and things can “bater certo” (be exact, precise, spot on).
There’s an example of Bater Mal near the beginning of this song by the Greatest Band Ever
Luso 