Several of the Aimpoints will last 3-4 YEARS continuous operation.
Look on Aimpoints website and read the specs.
Don't expect that from a Wal-Mart "el cheapo" though.
And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him. And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth.