asking this question for a mate

car drives fine been for norris map and check over and all came up good

anyway one night he got in his car started fine,
drove off and then all dash lights and rev counter died

car has been to auto electrician and no blown fuses or relats etc
battrey was showing 11 volts and advised alternator has gone down so,
put brandnew one on today
car started first time switched off and wont star again with battery now showing 9 volts
fluid leval in battery was very low but still now dash lights
any ideas
thanks