Car Cut Off And No Start

[avensis 1.8vvti 2001]

hi, i have a toyota avensis 1.8vvti y reg manual petrol; - basically my car battry has gone completely flat. i was driving halfway to work the battry light came on my dash and also th abs light, gradually the lights started to fade as if the battry was dying. the radio stopped working and the car had lost power to move, my rev meter was stuck along with my speedo. the car came to a stop, i tried switching the car on again but the battry had died. i replaced the battry with a charged up one that i had then that died too and the same thing happended.

can someone plz advise me if its the battry or the alternator or starter motor that is causing this problem.

i would b greatfull for any replies

many thanks

vali