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HVB discharge overnight

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6 replies to this topic

#1 OFFLINE   LRonDrunkard


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Posted 24 May 2017 - 09:34 AM

I've noticed lately with my 2014 C-Max Energi (27K miles) that the remaining battery percentage decreases overnight while sitting.  I've suspected this for a while so started keeping closer track of it.  Here's an example of what happened yesterday.


Drove to work in the morning and parked it. It had 82% of the charge remaining.  Came out 8 hours later and still had 82%.  Drove it to my next destination on EV mode and parked it with 72% charge remaining.  It sat for approximately 14 hours overnight (unplugged) and when I got in this morning - only 65% charge remaining.  The daytime high yesterday was 64 F and the overnight low was 54 F.  I'm sure the battery may have heated up a little and the fan had to engage some but would it pull that much power?  


I'm going to keep watching this to make sure I'm not losing my mind.   I'm baffled as to why 8 hours of sitting during the day there is no loss of battery yet 14 hours overnight, I lose 10% of what is left.


any thoughts or ideas?  I don't see any indication that anything is being left "on" (it doesn't seem you can "leave the lights on" with this car, anyway).


This is my first plug-in hybrid so I'm sure there are things about it that I do not yet know...



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#2 OFFLINE   bdginmo


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Posted 24 May 2017 - 09:39 AM

This is probably normal. There is a correlation between HVB temperature and SoC. As the battery cools you may notice the SoC drop as well. A 7% drop because of this effect seems a little on the high side, but it isn't unprecedented either.

#3 OFFLINE   Perry Knopp

Perry Knopp

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Posted 24 May 2017 - 10:36 AM

 Your car isn't abnormal. I've noticed this also. Also generally overnight when temps drop.

#4 OFFLINE   rbort


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Posted 24 May 2017 - 12:52 PM

I'm always the case if the temperature drops you charge level will drop if the temperature rises your charge level will go up. That's why it's not good to have the battery fully charged when it's hot because the charge will go up even higher than the maximum the car sets the limit to and cause damage.

I've been saying this for the past three years, I mean seeing it and I mentioned it before, so it's normal don't worry about it.


#5 OFFLINE   Levi Smith

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Posted 25 May 2017 - 05:33 AM

a couple things here.


As others have said, the battery SOC difference you're seeing is just the battery changing on its own and/or the electronic logic trying to determine the %.  



The bigger part I haven't seen mentioned is understanding how that battery could actually be used by a light being left on, etc like you described...  For the most part it can't.


If your car is:


-Plugged in, the fan is powered by the incoming power. No real way to discharge the battery other than like having the heater(possibly the AC) on and drawing more power than external can supply.


-Turned off: The big battery is physically disconnected.  Nothing to drain it.


-Turned on without pressing the brake: The big battery is still disconnected.  This is a good way to drain the 12V battery as it's trying to power everything.


So, basically the only way anything can drain power from the HV battery is if the car is fully ON.  But yes, the battery % shows losses almost every time I turn on the car again.  I'll attribute it more to software errors in trying to determine the charge level than anything else...



#6 OFFLINE   cwstnsko


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Posted 25 May 2017 - 06:05 AM

As others have said, the percentage reading changing is almost certainly due to temperature change.  The percentage charge is almost certainly tied to a voltage reading, and at a given state of charge the battery will read a slightly different  voltage, depending on the temperature.  I have no idea how sophisticated Ford has tried to get with this calculation.  I theory, it could be temperature compensated, but there is also the likelihood that the battery actually has slightly higher capacity to hold energy at warmer temperatures than at cold temperatures. 

#7 OFFLINE   tr7driver


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Posted 25 May 2017 - 07:41 AM

And that's why it is called the "Guess-O-Meter" 

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