Battery indicator changes after car sits

[Jjarman123]

I'm not sure if the battery indicator on the dashboard is for the 12v battery or the other battery but it will show almost full when I park the car and then sometimes after a few hours parked at work I will come out and it will be almost drained.  Car starts fine so I am not sure what it indicates or why it goes down.  It always charges back up after I drive a few miles.  I have replaced the 12v battery once about 2 years ago and had one instance where the car was dead and had to be jumped off.  Other than than no problems.

[ptjones]

The battery indicator is for the HVB and this changes after you let the car sit for a while. Typically the battery would be cooling off and I think there is some battery cells  voltage getting balancing out going on too. This is normal, what kind of gas mileage are you getting?

 

Paul

[Jjarman123]

I’m getting about 40-43. I called the dealership and he was honest and said he had no idea what it meant but tha tif it had been doing it since I’ve had it (bought it used 4 years ago) and nothing else going on it’s probably fine. He said even the hybrid tech probably won’t know because they work on so few of them. He did say they have never had to replace the hybrid battery on any of them so that was good to hear.

[plus 3 golfer]

Like Paul said the battery symbol is for the HVB. One must recognize that the symbol is showing the "usable" range of the HVB not the entire capacity of the HVB. The HVB capacity = 1.4 kWh (when new) = 100% State of Charge. The symbol shows from about 30% SOC of the 1.4 kWh to about 70% of the 1.4 kWh range or about 0.56 kWh (40% of the 1.4 kWh) when the very tip of the symbol is blue. See the graph below showing the approximate relationship between what the symbol shows and the "actual" SOC of the HVB. The typical range of HVB operation when driving is from high 30s / low 40s to low 50s % SOC. So, even if the symbol might drop 25%, the SOC really fell about 10% or only around 0.14 kWh.

 

Temperature will affect the capacity of the HVB but generally when ambient temps are higher there should be little effect (maybe 5% of actual SOC) based on curves of lithium ion cells.. I don't know how / when the Battery Management System adjusts SOC but it has to do such periodically to compensate for "drift" of the calculation methods it uses.

 

As far as cell balancing, the BMS, when required, equalizes the charge of the 76 cells that make up the HVB by draining charge from the cells with the highest voltage. This will affect SOC. There are many checks to ensure the HVB is operating most efficiently and to prevent damage to cells. There will be Diagnostic Trouble Codes thrown if these checks exceed thresholds. For example in the Energi’s 84 cell HVB, the BMS checks groups of 6 cells to make sure that the difference between each cell less the average of the 6 cells is less than 75 mV (0.075 V). A DTC will be thrown if this check fails. I assume that as cells age, the variation in cell voltage will increase and thus the loss due to equalization will increase and we might see a larger drop in SOC. With 113 k miles on my C-Max, it sure seems that I see more of a drop in SOC now than when new although I never monitored the drop.

 

 

Edited August 8, 2019 by Plus 3 Golfer

[fbov]

And to be clear for Jjarman123, the data plotted above was taken from your car through the diagnostic port using FORscan. It's not what "should" happen, it's what "did" happen. This design intent is consistent with requirements for Li-ion battery longevity. 

https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

 

FWIW, I just got a new robot vac, with Li-ion batteries. When running, it returns to recharge before dropping to 30%. Sitting in its dock, it's app currently reports 77% charge. Very reasonable for applications in environmentally controlled spaces. Ford is more conservative because cars have to live outside. 

 

Have fun,

Frank

[ptjones]

I’m getting about 40-43. I called the dealership and he was honest and said he had no idea what it meant but tha tif it had been doing it since I’ve had it (bought it used 4 years ago) and nothing else going on it’s probably fine. He said even the hybrid tech probably won’t know because they work on so few of them. He did say they have never had to replace the hybrid battery on any of them so that was good to hear.

I'm not aware of any HVB being replaced and with 232k miles on mine I think it is safe to say it will out last the car. :)

 

Paul

[oldloboy]

My problem with my 2013 hybrid, 96k miles on it ,is that it proactively charges the HVB occasionally overnight while the ignition is off!   This began occurring recently but often enough that I check and recheck that I have turned off the ignition when I exit the car.  What do you think of this "automatic" charging procedure?

  No, I do not have the Energi and I find the battery will be completely topped off even though the AA icon reads 25% when I switch off.  I suspect that the software is trying to extend the life of a rapidly aging HVG, but I'm only guessing.

[jestevens]

I have a similar mileage and age on mine and haven't really noticed an issue with the HVB vs the way it has always worked.  Since it wasn't throwing a code I wasn't really paying attention, just get in and drive.  The battery capacity is so small that you could only go a few miles on full EV so I consider it as more of a device that evens out the RPMs and extends range of the ICE. 

 

If the engine is not on and you have MORE charge than when you shut it off the night before maybe the ambient temps were extremely hot or cold and it limits the use of the battery - thus shows less available SoC at one time vs another?

 

When my Prius battery was starting to age you could see that it would easily go from empty to full in a very short amount of time with the engine running more - I think because less cells working.  That coupled with lots of high speed HVB exhaust fan noise prompted me to sell Prius and buy C-MAX while the battery pack still had SOME life left in it.

 

To really know what is going on you would have to chart it with one of the OBD diagnostic programs?

[plus 3 golfer]

...

 

When my Prius battery was starting to age you could see that it would easily go from empty to full in a very short amount of time with the engine running more - I think because less cells working.  That coupled with lots of high speed HVB exhaust fan noise prompted me to sell Prius and buy C-MAX while the battery pack still had SOME life left in it.

 

To really know what is going on you would have to chart it with one of the OBD diagnostic programs?

With over 100k miles on my C-Max, I do monitor SOC and usable energy of the HVB. My recording of data shows that the usable energy (kWh) is still over 0.51 kWh which shows as a SOC range of 34%-71% SOC, virtually the same range as new.

Edited August 19, 2019 by Plus 3 Golfer