battery capacity is going down

[zolorin]

So when I bought the car in September I recorded 18.5 kw-hr charge capacity. I had a long trip to Julian (see one of my posts), in November that I used up 17.7 kw-hr on an 80+ mile trip with 8% remaining. I did a whole bunch of short trips over the week and put it to charge and I was shocked when the car charted 17.1 kw-hr with 3% remaining. My charge times have reduced from 3.5 hrs to 2 hours. My driving range reduced to 68 miles (and I don't use heat, ac or crazy driving styles).

Has anyone had an issue with their battery packs?

 

[sefs]

If the ambient air temperature is below 60F, expect capacity to start going down. It will come back in the spring.

 

[michael]

The nature of your drive also matters. You can get more kWh out of the battery at low consumption (for example, 25 mph vs 65 mph).

This is totally separate from the fact that your Wh/mi is higher at high speed....the available kWh is also lower.

Why? because at high drains, more energy is lost to the effective series resistance (ESR) of the battery.

So to be meaningful, both trips must be comparable, and the temperatures must be comparable. Were they?

 

[epaminondas]

No one has verifyably recorded any battery capacity changes. That behavior is reserved for Nissan Leafs. From all acounts and from my observation, inconsistancy in range estimation of the GOM is directly rlated to the previous driving session. If you drive for 80 miles at 35 mph with the heater off, the GOM will reflect that behavior by giving you a much longer range estimate than if you just drove 70 mph with the heater on.

 

[WattsUp]

My charge times have reduced from 3.5 hrs to 2 hours.

Unlikely. The fastest time a stock FFE can be fully charged in is about 3.5 hours.

How are you measuring charge times?

If you're going by the durations reported in the log at MyFord Mobile, note that those numbers are notoriously often wrong. I've had full charges that "took" only a few minutes (according to MFM). More often, the reported times are off by some random amount (an hour, 30 minutes, etc.). I find the log to be completely unreliable.

 

[michael]

No one has verifyably recorded any battery capacity changes. That behavior is reserved for Nissan Leafs. From all acounts and from my observation, inconsistancy in range estimation of the GOM is directly rlated to the previous driving session. If you drive for 80 miles at 35 mph with the heater off, the GOM will reflect that behavior by giving you a much longer range estimate than if you just drove 70 mph with the heater on.

I would say it is certain that every one of us has lost capacity...this is a basic principle of all batteries. What I cannot say is how much, or even if it's enough to be observable without actual test equipment.

At 30,000 miles, I have the impression--and it's only an impression--that I may be down a kWh. but as we all have agreed, it's winter, temps are down, who's to say?

Absolutely the GOM doesn't tell the story. And the dashboard energy consumed meter doesn't tell the whole story. One of our posters suggested running the heater full blast with the windows open. This is probably as good as one can do, and even this method has the variable of battery temperature.

I have two friends with deteriorated Leafs, and I can tell you that in their case there is absolutely no question that the car is crippled. Just today, one of them told me he now has to charge his car late in the afternoon to make it home. If he charges earlier in the day, the battery sags enough during the afternoon that he doesn't make it! When new, this was an easy drive for him.

 

[hybridbear]

Remember that as the battery cools in winter it holds less energy as well which reduces your useable capacity.

Our Fusion Energi shows 7.1 kWh when fully charged at moderate temps (60+) but only about 6.4 kWh on a full charge when the HVB temp is 30-35 F.

 

[zolorin]

my charge time has reduced to 2 hours, but maybe you are all correct about the winter capacity -- lets wait till spring and then I will scream bloody murder

:twisted:

 

[michael]

The battery cannot fully charge in 2 hours if it has anything approaching normal capacity.

If you are concerned, I suggest:

Fully (or almost fully, say to less than 5%) the battery
Put it on a nominal 30 A charger
See how long it takes to fully charge.

It should take something like 3 to 3.5 hours (240 V x 28 A = 6.7 kW; 3 hours gives 20.2 kWh)

If you can fully charge in 2 hours, you put in only 13.5 kWh approximate, definitely not a full charge.

If you are getting anything like the normal range (70 miles) then your battery is reasonably normal.

 

[WattsUp]

my charge time has reduced to 2 hours

How have you measured this?

 

[hybridbear]

You can get an idea of how much electricity is going into the HVB by leaving the car on when charging and using a trip meter to measure how far it "spins backward". If your battery is near empty you can measure how much is going in for a full charge.

 

[GladeStorm]

17 kWh sounds like it is within measurement error of being fine (while being inconsistant with a 2 hour charge time).

Although use of the tripmeter seems to be one of the more accurate methods of checking capacity, there does seem to be some measurement error introduced during regeneration. [ I've tried comparing energy use with the "Energy-to-empty" parameter in the OBD; the numbers diverge somewhat during regen]. I suspect that Sefs method of static discharge (using the Climate Control) is probably most accurate: http://www.myfocuselectric.com/forum/viewtopic.php?t=2497#p17188

Back to the original question: I'm thinking that "normal" capacity-loss won't be measurable until somebody approaches the area of 100,000 miles. However, there have been a few cases of battery cell failure apparently due to manufacturing defect (mine was one of those). This problem appears to show up within the first couple thousand miles of use. I originally tracked my problem by logging a lot of data from the tripmeter and watching the capacity fall, but that's very time consuming and in hindsight there are a couple of simpler methods of determining if you have a problem. If you don't want to go to the trouble of hooking up to the OBD, the simplest is to look at the vampire draw. Normally, once fully charged and balanced, the vampire draw should be around 2.5 watts. (The service manual says that it can take up to 24 hours to balance the cells after it's reached full charge, but generally it drops out of balance mode pretty quickly). When a cell is going bad, the BECM will be stuck in balance mode (which draws about 35 watts) pretty much forever.

It's simpler if the temperature is above 50 deg F so that you don't have the TMS cycling, but the bottom line is that if you ever see the vampire draw drop to the 2.5 watt area (or the light on the 'convenience cord' stops blinking), then you probably don't have a faulty cell.

 

[Billy Bob EV]

I would think that Ford might have the capability of collecting data on each car, beings we can access that info on our smart phones? It doesn't bother me if they do, I figure it's for the good of improving EV's!

 

[michael]

Having reached 36000 miles, I just now intentionally ran the battery down using the heater at full blast. It reported 17.4 kWh when I got the SSN message and the heater stopped consuming power. The car would still move, but I didn't see how far. The test took just under 4 hours. Battery temperature was 95 at the beginning of the test and dropped to 87 over the duration. Final SOC was around 8%

I think this is a fair assessment of capacity, down perhaps 1 kWh (5 or 6%) over 36000 miles. By comparison, when a Leaf loses its first battery capacity bar, it's down 15%

My 5% estimate is right in line with the data shown at

http://chargedevs.com/wp-content/uploads/2015/02/Tesla-Model-S-max-range.png

for Tesla model S....around 5% loss at 55,000 km

 

[kmaluo]

I've had my car for exactly 2 years now, and have 26,000 miles on it. I take the same trip to work everyday, and here in Hawaii, temperature doesn't fluctuate too much. I used to be able to make it to work using 40% of the battery, now it takes me 44%. I don't think I drive any different from day 1. I'd say that's roughly a 9% drop in 2 years for me.

 

[WattsUp]

I don't think I drive any different from day 1. I'd say that's roughly a 9% drop in 2 years for me.

Hard to say. You're in the range (no pun intended) of that kind of delta still being attributable to something you are doing.

Have you checked your tire pressure? I get about 10% more range by running the tires at 45 psi instead of the stock 38 psi. (Lower rolling resistance.)

Or, have you changed the tires while you owned the car? Different tires could easily affect the range.

 

[jmueller065]

I agree: You can't really use the Guess-O-Meter to judge for battery loss. It could simply be the fact that you've now driven the car a while and know how to drive it to get the range you need out of it as opposed to when you first got the car and didn't know so you drove it as conservative as possible to get the most range...

 

[kmaluo]

I agree: You can't really use the Guess-O-Meter to judge for battery loss. It could simply be the fact that you've now driven the car a while and know how to drive it to get the range you need out of it as opposed to when you first got the car and didn't know so you drove it as conservative as possible to get the most range...

Is the battery percentage display that inaccurate? I keep my original tires at 42psi. Even if I drive my route as conservatively as possible, I only get a percent or two back.

 

[WattsUp]

I agree: You can't really use the Guess-O-Meter to judge for battery loss.

Is the battery percentage display that inaccurate?

Don't confuse the "Guess-O-Meter" (on the left-hand dash) with the battery SOC display (on the center MFT screen).

The GOM shows the estimated range remaining (in miles), and is only a "guess" rather than any kind of actual measurement. The percent SOC, on the other hand, is indeed fairly accurate, and is an actual measurement of the remaining usable energy in the battery. (Btw, the usable energy range spans about 8% to 90% of the absolute battery capacity, but the SOC displays this usable range as 0-100%.)

The GOM doesn't indicate battery capacity. It is just a (current) estimate of how far you can drive on the energy (currently) in the battery, based on your previous driving patterns (basically, your previous rate of consumption in simplistic terms). Thus, the GOM can only be regarded as a "guess", as mentioned, since the future driving patterns could be drastically different, and drastically change the estimate.

If your driving patterns are consistent, the GOM can be a very useful tool. If your driving patterns vary wildly, or suddenly change for a particular trip, the GOM becomes much less useful.

 

[kmaluo]

I agree: You can't really use the Guess-O-Meter to judge for battery loss.

Is the battery percentage display that inaccurate?

Don't confuse the "Guess-O-Meter" (on the left-hand dash) with the battery SOC display (on the center MFT screen).

That's what I thought. I thought Jmuller was calling battery SOC display a Guess-O-Meter as well because I was talking about percentage and not miles remaining. Overall, I'm still pretty impressed that the lithium battery has over 90% of it's capacity left after two years. There definitely is some noticeable loss though.