[T77911S]

17A is a lot.

did you do any work on the car before this started happening?

you need to pull fuses one at a time to see what is draining the batt.
you can also use a test light between the post and wire, makes it a bit easier to see from a distance.

the voltage is not important, just the current. you will have battery voltage even at the .25A.

starters dont short and drain batteries, not likely an alt either, diodes usually open. the windings could short, but that would give you a whole lot of other issues. if the alts output is fine, rule that out.
if the fuses dont leed you anywhere, check wiring problems.

again, have you done any work on the car?