2015 Prius on replacement battery not getting good mpg

Hi Folks
I have a 2015 Toyota Prius with a replacement battery (actually 2nd replacement - first replacement was defective and replaced for free). I am running stock dimension tires but they are by a company called Sailun (Trezzo h408 size 195/65). Since the 2nd replacement, in my usual commute of 10miles, stop and go with some hills, I've been lucky to get 40mpg. Usually I would get 42-45 but now I'm getting like 36-39. The car has about 150k on it. Weather is pretty mild usually except in summer when it hits 100 or more. Any ideas?

Thanks
Roger Elliott