I have been using the scales for over a year now and have not had to change the batteries

I bought it over a year ago and the batteries are still the same.

For 1.5 years with the same batteries.

At least six months. Maybe a year.

How long does a tank of petrol last in my car? That depends on how much I drive and whether I fill up with Super, Super Premium or regular petrol. The scale runs on AAA batteries. And they only cost a few cent.
If the batteries are a (financial) problem: there are also mechanical scales.