No I haven't disconnected battery.
I thought about the idea of gas having additional ethanol added to it, lately. It is supposed to happen, I understand. I bought gas at different stations lately, [ BP & Chevron ] & had low mpg with both. Car is in immaculate condition , but I live where 75% of my driving is on lever rural roads @ 55-60mph , & I need to find the sudden , large drop in mpg.