Gen 1 Battery Rehydrating Experiment Results

Thanks for the update. Glad to hear your confirmation that the dead battery module resulted from water loss.

(BTW, when the 12V AGM battery dies, a temporary rejuvenation may sometimes be obtained by adding an ounce or two of distilled water into the cells.)

DTC P3009 might also be caused by the traction battery ECU, the battery cable, the inverter, or the transaxle (MG1 or MG2). I recall that Art's Automotive posted good info regarding how to identify the component with the high voltage leak.

 

I'm impressed! GREAT JOB!!

I wished I'd thought of the self-threaded screws and plastic melt. The only change I would make would be to put the battery pack 'on end' and use only two holes per module. There is an alternative, one hole solution but that means the syringe has to inject water and remove the gas. The water can flow via the vent interconnect from cell-to-cell. Still, impressive job!

The main point is we're all at the 'bleeding edge' of Prius battery recycling and this is a good place to be.

You might want to get a megger tester to see if you can fault isolate the likely, high resistance bridge to ground. My only concern is the KOH is an excellent conductor, which is why we have to pay particular attention to sealing the case. (Gosh I wished I thought of self-tapping, stainless steel screws and plastic melt sealing.)

Bob Wilson

 

I'm still surprised that a 2007 battery pack would have failed under any condition. Makes me wonder if another scenario took place:

• The car sat unused for a long period of time
• the battery was drained too low by driving the car without gas.
• there is some other problem causing the cells to drain themselves inside the car (possibly the high voltage leak?)

 

Could be. In order for the cells to drain themselves, there would need to be at least two electrolyte leaks allowing a current path via the battery case.

Regarding the OP's discussion of very hot weather and its negative impact on the Prius battery:

The very first Prius problem I experienced was driving the 2001 in Palm Springs during the summer of 2006 (115 degrees F ambient temps), where the car had a no-start problem (DTC P3191). The Cathedral City Toyota service advisor told me that this was a common problem in hot weather and that if it happened again, I should get the engine ECU replaced. (They did not have the ECU in stock and we were just traveling through.)

The problem happened twice and my local dealer at the time, Rancho Santa Margarita Toyota, replaced the engine ECU at 59K miles under TSB EG011-03. That was the incident that prompted me to start learning about Prius and what could go wrong with this very complex machine...

Two months later the traction battery died at 61K miles, and was replaced by RSM Toyota under warranty.

 

Do you have any photos of a single module outside of a pack, where I could see easily where to drill holes for the boiling water injection? This is really interesting stuff. Might get some students into doing this on some bad cells, to see if they can recover them.

 

Thanks, I looked at them again, and finally found/counted all "6" screws.

Can't wait to do some experiments in NiMh Battery recovery. By the way, our EV Truck uses NiCd batteries, flooded with KOH, We use deionized water in them. Would there be any reason to use deionized over distilled or vice versa?

 

Good work, Jeff, with the 'drill baby drill'.

Texoma, if the deionized and distilled waters are both correctly labelled, there should be no difference. If you have a college handy, someone in the chemistry or biology departments should able to measure conductivity. The lower the better. Actually they could probably donate some very pure water to your effort with only a little coaxing.

 

Started experimenting with a dead module, the 5 cells measured less than 1mv when the experiment began. Note the 6th cell was destroyed in an earlier visual inspection:

 

Hi Mike,

The voltage is a little high for 5 cells. Have you measure the discharge, Ahr?

Thanks,
Bob Wilson

 

That was the voltage at the very beginning of the initial charge. I think the cell might need to be compressed, it was bulging on the sides when I originally cut into the first cell quite awhile ago. The module has been sitting outside for 4 to 5 months and was completely dry in all the cells. I suspect this would be a pretty good worse case example of a dried out module. If it's cells recover, with any capacity, I'll be surprised.

 

Ok, that is something I recently saw with a module I've been trying to rehydrate. I'm seeing:

• high back EMF - charging voltages are insanely high
• low capacity - we're talking 10s of mAhr ... milliamp hour!

I'm about to try some truely abusive things to see if I can get more normal battery function . . . discharge a cap into the battery.

Bob Wilson

 

Capacitor idea is interesting. Therefore, for grins, We connected a Pb/Acid battery desulphator (one of those magic, snake oil devices) to the 5 cells in the module under test. I believe it charges a capacitor to a high voltage, and then does a rapid discharge into the battery.

NOTE: I noticed you can dip your voltmeter leads (use old ones) into the electrolyte between the cells and measure the voltage of each cell. So far I'm seeing that the individual cells in the module are dramatically out of balance. Therefore, I'm going to use a battery maintainer, and the desulphator (even though NiMh doesn't have sulphation issues) to keep a constant flow of current through the module, hoping they'll eventually balance out.

 

So, can you tell me what the amount you ended up adding to each cell was,, and what is the current status of this project? Is your battery still up and running or did it die out again?

Thanks,
Zach

 

I know this is an old past, but thought I would give it a little bump. Jeffkay hope your rehydrated battery is still working. Any updates?
I recently replaced a couple bad packs in my 2001. I got about 800 mile out of the repair. Then the codes came back. It was another bad pack.
I tore the battery back apart. Your post gave me an idea. I weighed the packs. My packs all weighed in at 36.2-36.4 ounces. The three packs that were bad weighed 36.2, 36.2, and 36.3.
The three replacement packs that I bought on THE BAY weighed 36.7, 36.7 and 36.8. I realize that there may be factors that effect the weight other than drying. I also do not know the density of the original gel. If drying is the problem, .5 ounce difference in weight would translate to about 15ml of water.
I fear that the extreme temperatures here in WI may have played havoc with my battery. I am thinking about using your method it rehydrate my packs. I think I would start by just adding 3ml per cell. Any thoughts?

 

The problems I ran into:

1. sealing the hole used to inject the water - the Toyota/Panasonic patent mentions using 'plastic welding' and I even got the part and tool. But then I realized there was another problem I could not resolve.
2. dealing with a melted or compromised terminal "O" ring - there is a black plastic-rubber "O" ring, the path the gas escapes. Many times you can find the smear where they have effectively melted due to excess heat. I could never figure out how to 'refurbish' the "O" ring and achieve a pressure-tight, gas seal. Technical challenges include rates of thermal expansion and the small space. Perhaps if a new ring could be fashioned and embedded in a larger, plastic washer . . . maybe.

In the end, I decided it was easier to get NHW20 modules that have lower internal resistance (aka., less heat) and improved terminals rather than spend time trying to refurbish the old-style NHW11 modules. It just depends upon how you value your time and the quality of repair.

GOOD LUCK!
Bob Wilson