the battery dies everytime i turn off the car and i just recently put in a new battery, and also the last owner told me how he changed the alternator… what could be the problem:?: 
There could be many reasons. Check your belt, your alternator might not be charging the battery. Also check your wires, you might have a loose wire.
Also, are you sure it’s the battery that is dying. To check if it’s your alternator or you battery do the following:
Start your car (boost it or whatever)
Let it run for a minute or two
Then take off the ground/negative wire off the battery
If the car shuts off then your alternator is crap
And if the car keeps running your battery is crapping out, so you have to find out why.
Lastly, do your interior lights work. With certain cars, your interior lamps are burnt but the area in the door jam where the sensor is, is rusted. Due to this, the sensor does not work like it should and you are constantly draw power from the battery even when the car is off.
Try the above and see how it goes.