I got back from a 2 week trip.
I was careful to leave my FEH with a high charge when I parked.

I parked with exactly 52.7% on the Scangauge SOC meter.
I was gone 14 days.
I returned and the SOC was 45.7% before starting.

Exactly 7% charge lost in 14 days. ( or 0.5% per day )

It has been consistent like this the past couple of years.
I never had the ability to check for this the first couple of years.

I'm curious what other people are seeing.
I'm curious if this is calculated, or the FEH "assumes" 0.5% per day.
I'd like to know, how it knows the SOC lost being parked.
It will be interesting to know if this gets worse with age.
My 2005 FEH has about 117,000 miles.

 

Since there is no load, there's only one way which you probably won't agree with, voltage.

 

No load voltage at 52.7% = 339v
No load voltage at 45.7% two weeks later, 325v.

14v/250 cells = 0.05v per cell.

Does 0.05v = 7% charge?
Or did Ford lab test these 1000 times and find they average 0.5% loss per day and just use that as a basis?

 

Who knows "really" how the SOC is calculated! I say voltage, you say it counts days but what about warm days or cold days? Self discharge is less when colder!

 

I'm not sayin' anything. I'm asking. I'm asking other FEH owners who happen to also have SOC monitoring equipment to reply back with what they see in their own personal vehicles. If everyone reports 0.5% loss per day, that means something. If results are all over the place, that means somthing else.
Your hypothesis is one good one. Now we need more data.

 

The FEH battery is NiMH (made by Panasonic, I believe). Typical NiMH characteristic is self-discharge at a rate of 25% per month. The fact that you lost at only a ~15% per month rate is actually quite good. Note that the 25% per month is for battery only, not including monitoring circuitry built into the pack. However, the self-discharge of NiMH is high enough to completely swamp the monitoring circuitry. This won't be the case for new Li-Ion packs. Li-Ion typical self-discharge rate is very low, <1% per month, but expected monitoring loss is ~3% per month. This is a combination of the individual cell balancing and monitoring circuitry as well as the overall SOC / Temp / etc circuitry built into the pack. But 3% is a lot lower than 15-25%...RayP

 

Parking my FEH again @ 52.7%. Will see how close the results were to last time.

I've done more and more research into LiION and while they have more energy per pound, they do not seem durable enough for Hybrid or Electric car use. Expected lifespan is 3 years, and 36,000 to 50,000 miles, top end.

 

So, if they aren't any good why are they switching to Li-Ion? They are way easier to charge. I have a 1600mAH 17670 Li-Ion cell in a SureFire U2 Ultra flashlight for over two years without recharging and it still works. I have Li-Ion cells in other custom made LED flashlights with the same results.

 

This is old information. This is pretty much true for LCO and NMC types, but is generally not true for LMO and certainly not for LFP. The Volt will use LMO made by LG, and the Leaf will use LMO made by NEC, and while I personally don't trust their safety, their lifespan and range is way beyond what you are quoting. What I am waiting for is our US manufacturers to get going on volume production of LFP, which is going to revolutionize Lithium batteries. The latest research out of MIT on LiPO4 coatings on LFP crystals makes LFP nearly the perfect battery technology from a shelf life, charge lifetime, and charge rate perspective. Density is pretty good as well, far better than NiMH but still lacking compared with Li-S, Li-Air, etc. But those techs are still way too unsafe for any application, especially EVs.

 

SureFires are great, aren't they? Even the protected cells have a discharge rate of <3% per month, so after 2 years they should still have some life left. Unprotected cells are <<1% but of course they can explode on you if you aren't careful during charging, and are too easy to damage with over-discharging...