Anyone out there seriously looked at replacing the batteries in their battery packs? Higher capacity cell are available and would enhance the ICE off range. A look at the shop manual seems to say it would be possible and safely.

Not interested in answers that expound on warranty issues. I got it.

 

Swapping the cells may be the easiest part.
The hard part is re-writing the BMS, or battery management system.

At the bare minimum, you need to mimic Ford's, and inject your own data for battery state of health and state of charge.

To get more EV, or more battery boost at any speed for that matter, you need to "spoof" the Ford's system into thinking the battery is above 53% charged. At least in the 2005 to 2008 models, 53% is the prefered state of charge.

Any SOC lower than 53% and the car will use gas to try and build charge.
Any SOC higher than 53% and the car will use more battery and reduce gas use. 53% = stasis.

Otherwise, no matter how "big" your battery is, the FEH will only take out 0.4kwH and then put back in 0.4 kwH.

 

Do you own a spot welding rig for doing battery pack straps or battery impedance meter for testing quality of your work???

 

Yes. And I still call that the easy part. Plus there are dozens of battery companies who will do that for you at nominal cost.

 

These aren't your typical RC packs, so there are companies that would configure a couple of hundred cells or whatever is to a particular shape?

Does anyone know how SOC is calculated?

 

YES. ( The fairly easy part. ) Which means as long as you swap them out 1:1 if you get an old pack out of warranty, you are in good shape. There are currently dozens ( maybe 100's ) of people swapping batteries out of Hybrids, but they always swap a like for like. And I'm talking about partial pack replacement. Sometimes, for just a few bucks. ( or a few $100 )

YES. ( The complex part. ) Which makes it difficult to add additional battery capacity.

Do a little research. Show you are serious. Take "Doesn't Care" off your posts. I don't think you care at this point.

 

I know nothing about the Hybrid SOC but since you don't care to comment....

Most battery powered devices could care less about the capacity of the cell(s) or battery pack used. It's the max. voltage of the cell(s) or battery pack and as long as your still using Ni-MH, it's the same. The only exact way to know the what capacity is left in a cell or pack is to fully discharge it and you can't do that while the pack is in use. Since the Hybrid only use a small portion of the packs fully capacity, it "probably" a estimate and no need to be accurate. Swapping to larger capacity cells may be easier than you think.

Ah! Going to the larger capacity isn't without problem though! They don't tend to last that long. Take "AA" cells which were 1.8Ah and 2.0Ah max for some time then they started increasing. I still have 1.8Ah and 2.0Ah "AA" cells still going strong but my 2.3Ah, 2.5Ah and 2.8Ah all died a early death!

The bigger capacity cells tend to be somewhat bigger in size too! Sometimes one can barely get the battery compartment cover on some devices.

 

I think the SOC calculation is based on the stock battery pack capacities and voltages. I suppose if one were to replace the stock pack with batteries that had the exact same voltages and capacities, it MIGHT work. But it would not yield maximum results unless one could somehow reprogram the CPU to account for the actual characteristics of the new pack. And of course one would need data on exactly how the new technology would function in real life. Ford had this kind of data for it's packs - because they do years of testing under actual load conditions. But an end user would not have this information.

The FEH periodically re-evaluates the battery performance, and perhaps the software would make some adjustments based on the new pack cells. But it still would not achieve the maximum capability of the newer technology.

For the money, I would wait for the plug-in FEH.

 

Your FEH has a 5.5Ah pack right now. If you used cells that are twice the capacity, all that would mean is that at the same load, the higher capacity pack would maintain a voltage longer. The cells are nominal 1.2V/cell, fully charged around 1.4V/cell. Let's just say that the FEH keeps the between 1.0V/cell and 1.2V/cell. At the same load the higher capacity cells would be able to keep the pack between the limits longer.

I use to think it was better to run Ni-MH cells down low before charging but after reading in the forum about the FEH using such a small portion of the packs capacity and the constant discharging/charging, I don't believe that anymore. A Ni-MH is only good for so many cycles. Some say any discharge/charge is a cycle, other say the it must be a full discharge/charge cycle. The FEH battery pack's operation and lifetime sure proves that "any" theory incorrect!

 

Size issue: there are D cells out there with twice the capacity of the OEM Cells (eg 11,000 mAmp-hrs vs 5,500 mAmp-hrs)

So a D cell is a D cell is a D cell. Didn't mean to imply a different size cell in my post above.

Capacity & SOC: State of charge is measured by no load voltage which is a direct relation to the chemical makeup of the battery. There is probably an algorithm in place in the software that, given current loading, calculates SOC or capacity remaining from the measured under load terminal voltage.

Also, as the battery ages the capacity changes and the best way to monitor SOC with age is to use the batteries voltage. 5.5A-hrs may be 100% when new, but 100% at 5 years might be, say 4 A-hrs. You would have to periodically do a test discharge to determine true capacity with age.

The depletion of the chemistry inside the battery will depend on how much there is present. So, a higher capacity battery will deplete more slowly at a given current load than a smaller capacity battery. So replacing a 5.5A-hr with a 11A-hr d cell would be a good idea.

As I look at pics and the shop manual it would be a reasonable upgrade to consider at battery cell failure time. Doesn't look to me like welding is needed.

Regarding the SOC discussion there was a long and somewhat bitter thread on this awhile ago. Suffice it to say my words above are virtually the same as my position then and I didn't then, and still don't, buy some of the other theories propounded then.