crank sensor '90

replaced twice and battery dies slowly... anyone had this problem or know how to fix it?

Crank sensor has no bearing on batteries going dead. Look for a drain when everything is shut off, make sure the charging system is up to par, basic diagnostics.

Charge the battery. Disconnect the charger. put an ampmeter in line with the battery. You will see the current leaving the battery. Unfortunately, there are 100's of possibilites that can draw this current. I would start with the fuse panel. Remove one at a time and monitor the current. Then I would pull a relay out, one at a time, usually found under the hood. If you don't see a drain on the battery, I would suspect the charging system.