High voltage battery not holding a charge? (Hybrid city mpg dropping)

[Chris_G]

Q, sounds like you are on to something. Although you are starting out with a fully charged HVB. Yes you will be getting better mileage, i would think a DMM will help you further now. Start looking at that 12v battery voltage. To see if your problem is the charging of the 12v.

I started watching mine and i saw 12.35VDC the other day and that was the first time i took a reading, i am trying to figure a more permanent 12v gauge. Where i can keep record at a glance, instead of tilting rear seat and opening battery box and connecting leds. Hope this helps.

Okay, I'm confused, again. What does the 12 volt battery have to do with the high voltage batteries?

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[Eagle11]

No, go to the dealer, explain what you see and ask for them to interrogate diagnostics for any codes. My dealer will do that for free.

Love to see data from a hybrid with electric AC showing any mileage impact. I can't find it in my driving. My highest mileage is in the hottest months, but then, we call three 90-degree days a heatwave. You call it a weekend.

Currently, I won't get 600 miles to this tank, same commute, as always, the only difference is the heat and the AC on all the time.

 

[Mach 1]

Chris, the 12v battery is like the command and control, it runs the electronics and accessories which control the relays for the HVB? With most digital electronics theres a voltage threshold for reliability of the circuitry. If the 12v is not getting ample charge from the HVB then the circuitry becomes unreliable and i have seen some crazy operation from the circuitry, just a hunch at this point. I need to read up more on the components/modules/interface between 12v and HVB.

I was trying to offer the origin poster some ideas/checks he could do before dealership.

 

[Chris_G]

Chris, the 12v battery is like the command and control, it runs the electronics and accessories which control the relays for the HVB? With most digital electronics theres a voltage threshold for reliability of the circuitry. If the 12v is not getting ample charge from the HVB then the circuitry becomes unreliable and i have seen some crazy operation from the circuitry, just a hunch at this point. I need to read up more on the components/modules/interface between 12v and HVB.

I was trying to offer the origin poster some ideas/checks he could do before dealership.

Thank you!

 

[Mach 1]

Chris, did i BS you enough for you to believe i knew what i was doing/saying?

 

[Mach 1]

But yes, with a bad ground on the return voltage 12v battery, theres no telling whats going to happen, or what we will see.

 

[Shay]

Does AC have that much of an impact? I used to get 35-45 mpg around the neighborhood pretty easily, but now even when I turn the AC and radio off I get 28 if I'm lucky. Combined mpg since my last fillup is sitting at 19, and that's non-highway miles at <50mph

As with most hybrid vehicles, AC use has a massive impact because it is powered by the high voltage battery. Here in Phoenix I was getting 46 to 47 MPG City in the winter, I'm dropped down to about 31 to 32 with 100 plus degree weather and AC all day everyday. It's because of a few things. The battery is located outside the vehicle and subject to the heat, it has to power its own cooling equipment as well as the AC. Additionally, when it's over 100° or 110, the the computer will not draw as much power off the battery as when it's cooler so that it does not overheat. Because of this perfect storm of conditions, the gasoline engine has to work a much larger percent of the balance between the two.

 

[Eagle11]

As with most hybrid vehicles, AC use has a massive impact because it is powered by the high voltage battery. Here in Phoenix I was getting 46 to 47 MPG City in the winter, I'm dropped down to about 31 to 32 with 100 plus degree weather and AC all day everyday. It's because of a few things. The battery is located outside the vehicle and subject to the heat, it has to power its own cooling equipment as well as the AC. Additionally, when it's over 100° or 110, the the computer will not draw as much power off the battery as when it's cooler so that it does not overheat. Because of this perfect storm of conditions, the gasoline engine has to work a much larger percent of the balance between the two.

I'm seeing slightly better MPG than what you posted, but my MPG has significantly taken a hight with out high temps here in PHX.

 

[skinnyboy]

Hello all!

I have ~3000 miles on my hybrid XLT, and over the last 2 tanks I've noticed that my city mpg has dropped significantly (from 35-45 to 18-25), even though weather conditions & driving style haven't changed (90+ hot weather, tire pressure the same ~37 psi, city driving at ~45 mph or less, eco mode, etc).

Highway mpg seems unchanged (~33), but it feels like the Maverick no longer starts with any battery charge, and when it finally (after 1-5 minutes of driving) switches to battery, it lasts for less than 30 seconds before switching back to the engine (the size of the blue battery bar keeps shrinking until the truck switches), even if I let my speed drop to stay in electric mode

Any ideas before I reach out to the dealership?


EDIT:
Per Mach 1's suggestion, I attached a battery tender yesterday evening and it was still charging after a few hours, so I left it overnight. Woke up with the charging done, so I took the Maverick for a short city drive, and I was seeing much better battery performance, even with the AC on max. 14:48 drive time, 37.4 mpg, 7.4 miles total, 3.9 of which were electric. That's about what I was getting before the recent issues that dropped me down to 18-25 on almost the exact same route

I'll keep an eye on it for the next few days and see if it lasts

That's a big drop in fuel efficiency.

If the HV battery can't or isn't allowed to store this energy it will be lost to braking like a regular vehicle. Possibly an issue on your truck? Better hwy mpg than city kind of points this way.

A/C use will cause a noticeable loss in mpg, but not near this much, and both city and hwy.

It would be impossible for your 12v battery or electrical system to absorb and dissipate the kind of energy that would be the difference between 25 and 45 mpg. For reference, I saw an economy loss similar to yours on my Prius, caused by a stuck front caliper piston on the brakes. 15 miles home I had to stop every mile to put tons of snow on the wheel, it got wicked hot every mile.

Hope you find the cause.

Cheers.

 

[NewBernWolf]

Do you have hard data to back this up? I have data to disprove you..... BTW is was 114 here in PHX..

There's been pretty reliable data available for years that a/c in modern vehicles with the usual electronics makes very little difference in gas mileage. We live in the southeastern US, and our mileage is slightly better in the summer vs running the heat in midwinter.

 

[NewBernWolf]

Q, sounds like you are on to something. Although you are starting out with a fully charged HVB. Yes you will be getting better mileage, i would think a DMM will help you further now. Start looking at that 12v battery voltage. To see if your problem is the charging of the 12v.

I started watching mine and i saw 12.35VDC the other day and that was the first time i took a reading, i am trying to figure a more permanent 12v gauge. Where i can keep record at a glance, instead of tilting rear seat and opening battery box and connecting leds. Hope this helps.

Aren't there battery posts in the engine compart on the right side? I don't have the owner's manual in front of me, but I'm pretty sure that's where they are.

 

[fbov]

There's been pretty reliable data available for years that...

Here's some data for C-Max.

4 cars were run in Arizona for 600K miles over three years. The first half is flat, the second seems to show a pattern. A big effect should be consistent, don't you think?

Great data set BTW.
https://avt.inl.gov/

 

[Mach 1]

Wolf, there are posts by the ICE, i just accessed mine for the first time. Glad i did, the + is a pain to access, the cover is tough to wrestle, i am advising hybrid owners to know where they are and how to access them.

I thought it was easier to access the battery under the seat, keep my DMV on floor board.

I believe one of my first guage will be a 12v meter.

 

[troynm]

Okay, I'm confused, again. What does the 12 volt battery have to do with the high voltage batteries?

If the 12 volt battery is really low or not charging well it would start the ICE to charge the battery - right?

 

[Mach 1]

Troy, the hybrid electrical system is quite complicated, however the 12v system just runs accessories and computer. It gets charged from the HVB, whereas the HVB handles the ICE starting duties.

I was thinking if the 12v system is not charged properly that the computer could become unreliable in its operation and possibly not give the comand to run the relays that charge the HVB.

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