Burt, There is also the possibility that custody could be granted to him due to her violent behaviour - she obviously cannot control her temper and who's to say that she wouldnt lose it with a toddler?
Get your mate to talk to a Solicitor ASAP and move into a place of safety. The Police can refer him to the local Victim Support Group who can put him in touch with a local refuge.
If the violence really worries him and he's worried his partner may harm his baby, get him to take his daughter with him! The Police take a really dim view of spousal abuse and will deal with it professionally and will take his and his childs best intrests into consideration.
P.S, if he does take this further, the Social Services WILL be involved, so prepare him for that as well - hence my recommendation to contact a solicitor ASAP>
Good Luck
Flower xx