What , a simple cut to the head as grievous bodily harm? Never. The skin on the head , the skull, cuts very easily on impact. Agree it could be abh; there was actual bodily harm albeit nothing serious. Did the police see the injury? Did you get medical attention? The choice of common assault by beating ('battery') rather than abh may be one of evidence.
We don't know precisely what his record is but a second offence of drink drive in a fairly short time and with a high level reading, or serial drink driving, usually means prison in itself. That apart, and unknown, he may well get a short sentence in jail anyway. Domestic violence, threats to kill with intent that the victim fear that they be carried out, and the like, are regarded with disfavour by the courts. Beyond that, it's impossible to say.