Miles/km till tank refill mystery

Tacoma 2020,MT. Usual mileage about 450km/tank rural driving.Lately that figure dropped to 390km/full tank for last few months, no obvious reason. Anyhoot last week filled the tank for a planned trip. Km till need for refill gauge read 396km. Woke up to go on trip, battery dead. Took wife's RAV 4 on trip. Put in new battery when I got home and meter now says 571km till refill needed. I am going to check real mileage to verify. Any explanation for this phenomenon???I'm an old Canadian hence the going back and forth with mileage and kilometers, sorry, grew up with miles/gallons, last 50 years it's been km/liters.

 

Expected-until-empty is based on the complete history of fuel usage. Your history disappeared when the power vanished. Watch it drop as "real use" is encountered.

 

battery disconnect resets the fuel average computer so the more you drive it goes down

 

before it was averaging for lets say 50 tanks of gas but now it averages for just one tank

 

Buy a

$100 NOCO GB40 1000A UltraSafe Car Battery Jump Starter, 12V Jump Starter Battery Pack, Battery Booster, Jump Box, Portable Charger and Jumper Cables for 6.0L Gasoline and 3.0L Diesel Engines

NOCO GB40 to boost the battery next time. Perhaps your battery was end-of-life, but the battery boost should be able to get you back to a safe-point even if the battery is not exactly healthy.

 

Also, could the inimical reduction in mpg be tied to the transition to winter gas?