Casio - FX-82MS. I bought it in high school, used it in University and now on my 4th year as a Professional Accountant. Haven't changed the battery once. : r/BuyItForLife
Casio Scientific Calculator Model FX-300 (Solar) – Electronix Express
fx-820MS | SCHOOL & LAB. | Calculators | CASIO
Casio FX-300MS Plus 2 Scientific Calculator - SchoolMart