With all the discussion about batteries and state of charge, I was wondering:

The SYNC/NAV system has a rudimentary State of Charge meter built into the "Information/HEV" section, on the "Energy Flow" screen. The HV Battery icon has a little "fill level" bar graph on the right side. On my vehicle I've noticed that it almost always reads in the middle, with 5 of the 10 bars illuminated. Sometimes (after regen. braking down a long hill, for example) it goes up to 7 or 8, and after sitting idle with the A/C and accessories on it drops to 3 or 4, but most of the time it's right in the middle.

I wondered what this meant, and why it never got all the way to the top. The manual says:

Here's the picture from the manual. Their photo is kind of dumb, they show it as though the HVTB is "empty", which is not something you should ever see in normal operation, so I added some little lozenges in Photoshop to indicate the way mine usually looks, with 5 bars out of 10. They also show the outside temperature as -40 deg. F., so the people who wrote the manual must work in Alaska. No wonder they're listening to The Weather Network.



SYNC/NAV Screen, Information section, Energy Flow display

I was worried that my display reading in the middle and never getting "full" meant that something was wrong with my battery, but the manual says that's A-OK. I'm a little bemused that Ford thought the best way to indicate a properly-functioning battery was to display it as "half full" while you're driving around. Why not have the gas gauge read in the middle when you fill up the tank?

I know, I know. We're all supposed to be meticulously diligent Hybrid vehicle owners and RTFM.

Now the question: I guess this means my HVTB and charging system is working the way it should. How well does the display correlate with the actual health of the battery? In other words, how predictive is it? Does it keep showing in the middle of the display right up until the day the battery conks out?

 

It in no way corresponds to the "health" of the battery aside from it's behaving as intended, but that may be true even with significantly diminished capacity. A CHANGE in behavior with no changes to driving environment may indicate potential reduction in battery health. Gauge going higher and lower or doing it faster than before may indicate decreased capacity/health.

Your bemusement can be diminished by a rudimentary understanding of how a hybrid works. A hybrid vehicle is a gas car with an electric energy recover/release system. The hybrid battery is not a reservoir upon which to provide electric driving range. It is a reservoir 1) to store kinetic energy recovered from braking and 2) to release stored energy during gas-engine high inefficiency/demand phases. If the battery is full, you would defeat function 1, and kinetic energy would be lost during and converted to heat during braking. If the battery is empty, function 2 is defeated. Defeat of either function diminishes overall efficiency. Every joule of propulsive energy in the vehicle ultimately comes from gas.

Additional factors:

• Battery efficiency is near 100% in the middle of the SoC range and tapers off substantially at higher SoC and produces unwanted heat, so fully charging the battery would decrease overall economy.
• The more of a battery's capacity is used in a charge/discharge cycle, the shorter its life. If the full range of a HV battery were used, it would likely wear out in 2-3 years.

Your analogy to the gas gauge is absurd. The intent and result of the of the gas gauge is to provide you with a meaningful indication of the quantity of fuel. It is no different for the hybrid battery, and they document it. The only issues here are your assumptions and lack of understanding.

 

Thank you! That was fantastic! I've never felt so good about my analogies being absurd and having my assumptions and lack of understanding corrected so forthrightly! Actually, I do know that every joule of propulsive energy ultimately comes from gas, because it's obvious, and that the battery is there to store and release it, but you answered my real question perfectly. I just bought a 1-yr license for Forscan and I intend to use it and learn a lot more about the vehicle in the next few months.

I think it would great if Ford published your exact description on the first page of the manual, to make it very clear to everyone what the hybrid system does.

 

It has often been suggested that I should try some light beating around the bush. I might sound less d!ckish.

Forscan is pretty incredible. I've done 5 FEH/MMH with discharged batteries in the last few weeks, and it's superior to my $2,000 Snap-On Ethos Pro.

 

It's perfectly fine by me, I know I'm new to hybrids, plus I have thick skin and I've seen Full Metal Jacket a half dozen times:
"Because I am HARD, you will not LIKE me. But the more you hate me, the more you will LEARN!" - Gunnery Sergeant Hartman .

Seriously, I know that you must get a lot of super-dumb questions that people could answer themselves with a tiny amount of effort, both in your shop and here on GH, and I appreciate the answer because it's correct, and that's the most important thing to me. Particularly when the expense of a replacement HV Battery is looming at some point in the not-too-distant future. I also appreciate people who have in-depth engineering-level understanding of complex systems and don't beat around the bush. You're doing this for free. A lot of people wouldn't. My father's an EE/IE and he does the same thing. He was educated back in a time when professors weren't scared of hurting their students' feelings by telling them: "You can't solve the problem because you don't know anything and you're not working hard enough." It's not a character flaw.

I'm looking forward to grokking Forscan, the FEH is kind of a rolling science lab for me.

 

Heh... FMJ just came up in conversation the other day. We decided the kids are old enough to see it...

 

The FEH was designed to operate from 40-53% SOC. It was designed to hold at 53% SOC. On a downhill, MG2 will act to provide additional charge to the battery pack but at a reduced rate. Once the SOC reaches 60%, this type of addition is further reduced as if you can not add anymore. The vehicle is designed to burn off this excess SOC and will return to operating at 53%. All this can be monitored with third party hardware such a scanguage II.