Why is the fuel efficiency of my 2013 Prius decreasing?

Hello, in 7 years, it's expected that your battery capacity will slowly deteriorate. Think about your mobile phone -- do you get as much power out if it a year old, or when it's new? Same idea. Batteries are not exacting products. You can expect economy to decrease with age and wear. Naturally, things like air filters being dirty and spark plugs being worn can nominally affect economy also, so check that out. www.repairpal.com/repair-shops