I have bought a new battery for acer 4315. it is

i have bought a new battery for acer 4315. it is supposed to be original part, but laptop will not accept it. the computer will run if i first plug in to mains and the disconnect after it loads up, but will not start up on battery. there is a warning and thenn shuts down. when it is running on battery it does not detect that there is one. i have tried more than one battery. i have heard that the problem could be with vista- any ideas ?