Those with low SOC issues may want to check the interior dome light.

TL;DR: I've had intermittent low SOC issues and a dome light that hasn't worked correctly. I thought I'd switched the light off, but found that the contacts were bent. I suspect this led to a drain on the batteries. Since bending the contacts back in shape, I haven't experienced the same SOC drain.


I've had intermittent low SOC for a couple years. Sometimes I'd have low SOC (~20% monitored from the iPhone EngineLink app) after 12 hours or more of not driving, but sometimes I wouldn't. I've read through these forums and posted about it and suspected it may have been related to temperature or my driving habits (usually low mileage, but sometimes I'd still get low SOC on a Monday after driving 200 miles in the weekend prior). My 12V battery tested fine, the HV battery always charged up to and maintained the normal SOC range, and there were no other driving issues aside from the slow acceleration & regen during the first several miles when driving on low SOC.


I have had issues with my dome light for a few years (it wouldn't always come on when I opened my doors), but it was one of those minor things I ignored and forgot about because I parked in a well lit garage most of the time. I just switched the light off. Last week I decided to tackle the dome light and in the course of some online research in how to access and disassemble it, I learned that there are some relatively common issues with bad contacts in the light. Also with mine, I realized that I'd bent the contacts to the point it wouldn't even switch properly. I managed to bend the contacts back without removing the light (one wire is soldered on mine, unlike in the videos I saw so I didn't want to mess with resoldering upside down). Since then, my SOC has only dropped ~1.5% or less when it has sat overnight or longer. There could be other issues, but given the state of the dome light contacts, I think there was some low level drain on the battery from that light.



Hope this helps some people here.

 

The interior lights are on a "voltage minder" circuit that turns off in about 20 minutes after key off. So even if a light is left on it gets turned off automatically. So I'm not sure how any interior light could drain the HV battery. You could test the voltage minder function on your FEH by leaving the dome light on and confirming that it does turn off in 20 minutes.

 

That app looks interesting, but there isn't much information on it. I don't suppose you would give us a quick review?

 

You're right, there isn't much information on it and that's one of the main issues.

I bought the app (maybe $10?) about 2 years ago and a Bluetooth OBD reader (about $35). It has basic functionality and code reading. When I bought it, it did not have Ford Hybrid PIDs but I found some info online and was able to make a custom PID list in CSV format, programmed from PIDs from the Android Torque app. Since then the EngineLink app has been updated with Ford Hybrid specific PIDs, however I suspect these aren't entirely accurate. For example, the 4 HV battery PIDs all read the same data with the same equation, thus displaying the same value.

There really have not been many updates for the app or to the developers website or app wiki. At the time it was a very economical way for me to monitor, but I wouldn't recommend it. There are other OBD reader apps that might be worth checking out, but I'd probably just get a Scangauge now. IMO, given how iOS updates go, you can't always count on app developers to maintain and update their apps.

 

Hmm... I thought I'd read that a possible issue could have been a drain on the 12V battery leading to a drain on the HV battery. I thought this might include lights as well; I don't recall reading about the voltage minder. You are right, I did leave my lights on as a test and they shut off within 20 minutes. After the voltage minder is activated, could a bad connection reactivate the circuit? Just curious. If it wasn't summertime in Texas, I'd sit in my car and experiment.

Fixing the dome light is the only thing I've done to my car recently and since then, I haven't had any low SOC issues. I do have a vacation coming up so I'll see how it is after several days.

 

Hmm, that's certainly a possibility. I'm not sure what resets the battery minder, but I think it might be a door opening or ignition key. I'll try to experiment with that. Good idea though.

The HV battery can be discharged by leaving the headlights on, key off. I intentionally ran the HV battery down that way once. Once it gets below a certain threshold, maybe 25% SoC, there is no EV boost when driving. On ICE only the FEH is very noticeably struggling to move.

 

Just an update.

I bought a used pack from LKQ on 6/5/17 (From an 07 120k mi) installed it myself.
As of 11/25/17 its been back to normal. 48-53% most of the time; not draining randomly.

I suspect my year of ignoring the hot AC did some damage to the cells.

 

I missed that bit. I would say that's almost certainly the case. The key to the FEH battery reliability is its robust cooling system.

The HCH2 uses the same Sanyo Cells, and their reliability is crap because the cooling system is "meh" at best. While it move a LOT of air, it doesn't have a dedicated evap for cooing, and it maintains too high a temperature.

I personally cooked an HCH2 pack over a Phoenix summer by trying to hypermile the crap out of it. Was hitting 51-53mpg reliably in combined driving (truly 50/50 highway/surface streets), but it totally wasn't worth it.

Failure mode was the same... excessive self-discharge.

 

Would excessive self-discharge be at a consistent rate?
My low SoC happens irregularly, maybe once a month it will go to 17% overnight, but the rest of the time SoC is stable after days of non-operation.

 

Not always, but in the case of widespread heat damage, yes.

My '05 FEH exhibits this as does about a dozen HCH2 packs I have personally tested.