cbrown747 Report post Posted February 13, 2016 Does anybody know if a weak or failed accessory battery affect mpg? I noticed my mpg suddenly dropped from around 46 to around 41 over the past several months. I have owned my ford fusion hybrid 2013 for 3 years in florida and have the same driving patterns, but could not get an answer from the ford dealers. They blamed it on more ethanol in the gas. I researched that and could not find anything on that. I was in for an oil change and asked the dealer to check the accessory battery because my car would not stay in accessory mode listening to the radio before turning off.They found a bad cell in the battery and had it replaced and low and behold, my mpg has jumped back up. Quote Share this post Link to post Share on other sites
ElectricFan69 Report post Posted February 14, 2016 Does anybody know if a weak or failed accessory battery affect mpg? I noticed my mpg suddenly dropped from around 46 to around 41 over the past several months. I have owned my ford fusion hybrid 2013 for 3 years in florida and have the same driving patterns, but could not get an answer from the ford dealers. They blamed it on more ethanol in the gas. I researched that and could not find anything on that. I was in for an oil change and asked the dealer to check the accessory battery because my car would not stay in accessory mode listening to the radio before turning off.They found a bad cell in the battery and had it replaced and low and behold, my mpg has jumped back up.The mechanism I'd see is the ECU 'forgetting' its adaptive learning due to low voltage. Doing so would wipe out the 'near home' EV capability, have it use the 'default' settings for timing, etc. Now, I'd also expect to see things like failure to start and random ECU error codes. Quote Share this post Link to post Share on other sites
lolder Report post Posted February 14, 2016 Did you have a "cold snap" when the mpg fell? Mpg goes down 2 mpg per 10º F. temperature drop. That would be about 25º in your case. Quote Share this post Link to post Share on other sites
DannoMcK Report post Posted February 14, 2016 Does anybody know if a weak or failed accessory battery affect mpg? I noticed my mpg suddenly dropped from around 46 to around 41 over the past several months. I have owned my ford fusion hybrid 2013 for 3 years in florida and have the same driving patterns, but could not get an answer from the ford dealers. They blamed it on more ethanol in the gas. I researched that and could not find anything on that. I was in for an oil change and asked the dealer to check the accessory battery because my car would not stay in accessory mode listening to the radio before turning off.They found a bad cell in the battery and had it replaced and low and behold, my mpg has jumped back up. A dying low-voltage battery is known to the Prius community to cause a drop in gas mileage until replaced. (I just traded a 2006 Prius for a 2016 FFH Titanium. Hi!) I presume that the hybrid system wastes energy constantly trying to charge a battery that is worn out and ultimately won't charge. It wouldn't surprise me that the Fusion Hybrid is subject to the same thing, but it seems like something the dealer would know about. Quote Share this post Link to post Share on other sites
