I have a 2014 CRV-----43,000 miles. The battery died in a Walmart parking lot. I naturally had the Walmart people replace it.....1 month ago.

I was getting 31 mpg---average.....I am now getting 26. What could possibly happen in just changing the battery????????

 

welcome to the forum. only thing I can think of is alternator draw, or a/c draw. do a load test on the battery to see if it is in good condition.