I've got an FEH with a big ol' NiMH battery that's about 2.5 years old and a EV drivetrain that has the guts of a Prius Type I. Since older Prius batteries are similar to mine, what are users experience with older, high-mileage batteries? Have drivers experienced a decline is performance/efficiency that's noticeable to the driver? (that is, without a multi-meter and bench experiments!)

 

In general, there have been very few problems with the Traction batteries in Prii (some connector corrosion events in the 2001-2003 models). My 2004 is at 106,000 miles and no problems. Prius batteries are made by Panasonic. Yours are not, so YMMV.

JeffD

 

I would recommend reading the Dept of Energy studies:

http://www1.eere.energy.gov/vehicles...d_library.html

What they found was after 160,000 miles, the Prius batteries had gone from 6.5 Ahr to 2.5 Ahr. Yet even with this decline in capacity, the vehicles were still getting nearly the same mileage at the end as at the beginning of the tests:
http://www1.eere.energy.gov/vehicles...ife_test_1.pdf

I've got four from another Prius salvage and they all measured 3.3 Ahr. This weekend, I'll pickup up a failed battery pack, two know failed cell assemblies, and will begin testing those cells. I'll also do a failure analysis of the two failed packs.

Bob Wilson

 

What have you done with your "pile" of Prius Hybrid Batteries? Are you going to rig two of them together in your vehicle in an attempt to get longer EV?

 

Following example shows 349,531 Miles with the original HV battery.
http://john1701a.com/prius/owners/jesse4.htm

Ken@Japan

 

Right now my interest is in module refurbishment:

This chart shows the effect of replacing the lost water from two NHW11 battery modules and successive discharge-charge cycles. As you can see, I'm taking used battery modules at 2.2 Ahr and with water replacement and reconditioning discharge-charge cycles bringing their capacity up to a little over 6.5 Ahr. Here are few more photos showing some of what I'm doing:





My thinking is if we can refurbish our worn out battery modules for $5 in parts and water, for ~$200 plus labor, we'll be able to significantly extend the life of our hybrids. It looks like about $100-300 in special tools and a well written instruction manual, any reasonably skilled, 'do it yourself' mechanic can refurbish their own 2001-03 Prius battery. Best of all, this approach puts a permanent service plug in each battery module so annual or bi-annual water replacement will keep these batteries running until the wheels fall off.

BTW, the battery recharger, if done right, can also work as a plug-in lite. What this means is in the evening, the 2001-03 battery can be safely tickle-charged to 80% SOC and at the same time, the health and status of the individual modules checked. This will give the owner-operator a 'boost' during the next day's warm-up and an early indication of marginal modules.

So what'ca think? Right priorities?

Did I mention I have one NHW20 battery module and it looks like a well designed system will also work for the 2004-current Prius.

Bob Wilson

 

Plug in lite? Poor Mans plug in? Wow! We want to learn more. Keep us updated.

 

Exactly right! IMHO this is an aftermarket that is going to happen. It's only a matter of time.

Bob, are you thinking entry here -- have you worked on supply chain, markets and venture capital? ... want to?

 

Hi folks,

There are still a lot of puzzles to figure out before we go too far on this. Also, my guide has been a number of patents that need to be acknowledged and terms worked out. But these preliminary experiments are promising.

Some of the challenges that remain:

• best material for the service plug - it needs to be impervious to 6 M KOH solution yet support easy service by simple tools.
• how to install - a type of 'heat welding,' the service plug needs to be able to handle the maximum pressure of the existing safety value
• refurbishment procedure - I'd like to use a single service plug instead of the two in the current approach. The challenge is to normalize the replacement water across all cells and this is not trivial. But I think I have trick that will work.
• accelerate normalization or 'in car' process - I'm normalizing the cells with a 'discharge-charge' using an RC model battery system. This may not be the best approach. One other patent references using an elevated temperature and there is another charge-discharge pattern that might also help. We are essentially 'activating' the electrodes and this is not a trivial problem.
• proof testing - any refurbished module needs to be proof tested to make sure it won't fail in abusive conditions under cold or heat stress. This is not trivial since the failure mechanism can look like an electrolyte grenade or run-away hose spewing a stream of concentrated electrolyte. . . potentially very dangerous!
• investigate electrode leaks - it may be possible to decrease the maximum module pressure with a less strict valve and avoid electrolyte leakage around the terminal plugs. This would require more frequent water service but now we have a service plug!

There are lots of problems and issues to figure out. However, sharing what we've already learned will maybe encourage others, those who have some skills in this area, to collaborate. Then maybe we can come up with a kit that would allow folks to refurbish their own battery packs safely with a reasonable expectation of success.

FYI, the "plug-in lite" works on the principle that there is a maximum charge that would cause the control computer to see the traction battery as "at 80%." This means the control laws would try to use that extra charge to bring the battery closer to 60% and hopefully, do this by doing more EV and less ICE assisted warm-up. The nice thing is we are simply using the reserve capacity already in the battery so we start off each day with a peak charge.

Done correctly, the "plug-in lite" charger also monitors the health and status of each module during the 'top off' charge. It might also do some battery temperature management to try and keep the battery pack "not too cold" and "not too hot."

Interesting stuff.

Bob Wilson

 

Great work on the battery refurbishing.
Any progress on the failure analysis of the failed battery?

Thanks Andrew