iveco daily 3510 starting problem or alternator?

hi everyone, i have bought iveco daily year 1999/2000 and have a problem with battery - nothing worked, no electricity at all, so i tried battery from my rover 416 and it worked OK, i have bought a new heavy duty battery but when i start the engine now the battery indikator doesnt go off. Does it mean that alternator is not working? I am wondering if it cant be just some fuse or relay, or if the alternator is gone as well. Could you please help me