Wouldn't AVG_SOC be the average over time and the SOC at the current time. AVG would say that the pack isn't discharging which it might not if the thing keeps overheating.

 

Given that the battery spends the vast majority of it's time in normal operation at approximately 50% SoC, and the car actively seeks to maintain this, and the car will never achieve this 88.5% SoC in normal operation, I can't assign any reasonable meaning to an average SoC of 88.5%.

Additionally, while it can be throttled aggressively, discharging is throttled less than charging. Charging when hot causes far more damage than when discharging when hot. If a hot battery is actually at 88.5% SoC, it will bleed it down until is in the 50% range.

The more common issue with hot batteries is excessive discharge and no charging resulting in very low SoC.

 

I can vouch for some of this in an anecdotal way with my experience, consisting of just one battery pack - the one in my '10 FEH without the rear A/C evaporator. This past summer during the hot days, even with my Heatshield sunshade on the windshield and using MAX A/C as soon as I got in the car, my average mileage over several weeks at a time began to dip into the high 20s, with readings like 26.5-28.5 being commonplace. The battery simply was not providing as much power for acceleration, EV mode and so forth, and it self-discharged down to 1 or 2 "lozenges" on my SYNC/NAV "Information" screen several times. Now that the weather has cooled down somewhat, I'm seeing readings of 31-32 MPG again, even driving quickly on the highway at speeds of ~80 MPH. There has been no change in my driving habits.

The obvious takeaways are: 1) Heat is more problematic for these battery packs than cold 2) These batteries have an optimal temperature range and keeping them there improves their operation and the MPG you will see and 3) Curse Ford for deleting the rear A/C evap. on the 2010-2012 models, which has likely shortened the life of my beautiful ~66,000 mile perfectly-maintained FEH Limited by at least a year or more.

 

Question for folks who know more about the HV battery. Checking the BSOC and VPACK before and after the car sat for 24 hours, I noticed the BSOC dropped about 1%, but the VPACK dropped 11 volts, from 344V to 333V. Is that a "normal" voltage drop? How low can the VPACK be and still start the car and run it past the ~45 second "warm up" time, so the car will start charging the HV battery?

The original failing battery would race the engine around 10 seconds or so after starting while backing out of the garage. I'm guessing that was because the VPACK had fallen under some set voltage for safe running off the HV battery. I didn't know about FORScan at that time.

I noticed FORScan reports up to 20 amps being drawn from the HV battery during the ~45 second warmup time. The BCM log showed the HV battery current surge when starting the engine at 40,806 ms, and the first negative (charging) current at 87,984 ms.

 

Normal-ish. Many variables influence it, but consider that 11V spread across 250 cells is only 0.04V/cell or 1.376 to 1.332 - a pretty negligible voltage drop on a cell basis.

NiMH is like lead acid. Voltage settles once current is halted. There is no reliable voltage to SoC relationship unless both current and temperature are considered, and you have the experimental data to generate the look-up tables.

I have seen successful starts at 305V - nearly empty. I have seen failed starts attempted at 285V.

I have never observed any "45 second warm-up time." I have witnessed charging begin almost immediately after ICE start on many occasions.

 

Well the saga continues... Monday Greentec came out and replaced the battery with a new 36 month battery. This battery immediately failed the BCM self test with the same P0A81 hybrid battery cooling fan control circuit code. Other than that, the car ran fine.

They also had a 12 month battery with them for delivery to another customer. I asked and they agreed to try the 12 month battery to see if the problem changed. Initially the 12 month battery gave 3 codes right away when scanned: P0A81 (fan 1), P0A96 (fan2) and B1239 (air blend door)! After some phone calls it was suggested to clean the 40 pin HV battery plug (I know, only 28 pins are present). After cleaning the pins in the connector, the battery gave no codes. Even the BCM Self-Test ran without any codes!

They put the new 36 month battery back in, and P0A81 came back. They cleaned the plug twice more, each time the P0A81 code came back. The car runs, but I'm worried the battery could overheat and stop again with Stop Safely Now. They have battery #5 on order. No ETA yet. Very frustrated! This is ridiculous.

 

They are just burning their own money not checking the fans. For all we know some tech is leaving the fan unplugged.

 

Or, the rebuilders know they have cheap battery cells from who knows where and are just hoping that their replacement pack will last long enough until the customer gets rid of their car. A problem is that the battery suppliers have moved on to Li-ion batteries for these applications.

 

Doesn't sound like they are winning with that strategy. The warranties are for 1 to 3 years. If cells work that long chances are they are ok.

 

While they are inferior in quality, there's nothing "cheap" about the cells. All cells come from one of two cell manufacturers China. The problem is that one must invest much time and labor in testing what comes in from China because they won't hesitate to ship non-conforming product when they have quality fallout at their end or mis-matched product. The builder has to balance quality measures and profitability. In many cases is it dramatically more economical to fix the 10% of garbage that comes in after-the-fact rather than test 100% of the incoming product and take the hit to the bottom line on all packs.

On an individual basis, it doesn't seem like they're winning, but when you consider that they're doing fine with 90%+ of the packs that don't exhibit problems, it's definitely a winning strategy.

I don't deal with packs built from "D" cells except in my personal "collection." I like making more than minimum wage when working on batteries.