I have an RF-B45, the B65's later cousin, and my RF-B45 is not terrific on batteries. Slightly different circuits from the RF-B65, though....
I have never measured the hours the batteries last on my RF-B45, but I have other, similar radios (Sangean brand SW radios) that have longer battery life (the Sangean 800A is an example).
I found a review of the RF-B65, and in a comment below the article a guy says that his RF-B65 "really went through batteries fast".
So maybe your radio is OK. It just uses batteries more than other radios do.
Here is the review. The comment I mention is at the bottom of the review:
https://swling.com/blog/2017/04/the...portable-with-a-cult-following-amongst-dxers/