Re-hydrating the battery modules.

The above are potassium hydroxide and sodium hydroxide respectively? Excuse me, swear I didn't google it, just wanna test my battered old brain cells.

Also, what would happen if the cells could vent freely, say via a pin hole, they'd quickly dry out?

 

John the red pads are very thin O,13 mm thick and appear to be a type of plastic tape that runs around the battery - I pulled a piece off to measure it.

Roy

 

I drilled and filled a couple of 2004 GenII modules, which had 200K miles on them. They were low in capacity, based on Techstream, but I don't have the charger to accurately check them. Once one gets setup, it take less than 10 minutes to do one module. It went much as John describes in the first post, with each module taking close to 60ml, maybe a bit less. I used a 1/16" (1.6mm) drill. Both were bone dry initially.

I popped the relief valves without issue. I found that they released around 110psi (7.6 bar), or maybe a little less, using my shop air compressor with a not terribly accurate gauge. I clamped the modules in a vice with wood blocks which completely covered the faces.

My level checking setup is shown in the picture. I used a high value resistor (1Meg ohm seems to work, less is OK) across the DVM leads. The negative voltmeter lead goes to the negative of the module. The positive lead goes to a small gauge solid wire, whatever can fit in the holes. The insulation is left on the wire, so that only the cut end of the copper comes in contact with the electrolyte. The wire is pushed into the hole and the voltmeter will show a sudden increase in reading as the fluid is contacted. It seems that I ended up with just a few millimeters of fluid above the plates. However, I am thinking that level will change as the battery charges and rehydrates completely. So I will keep checking as I go. They are charging, with the drill holes open for now.

I was thinking, as I mixed the KOH, that John's suggested concentration seemed high. Over time, if a large amount of KOH was actually expelled from the module, there would be evidence of white powder in the vent tubes, and rather more corrosion than what is seen. Surely some electrolyte is expelled, judging by the green interconnects that are typically seen in older batteries, and we can only guess at this point, but I think that it is mainly water that is lost. I ended up using half of the concentration of KOH that John suggested, just to see what happens. I got my KOH from Essential Depot: Sodium Hydroxide, Lye, Potassium Hydroxide, Argan Oil, Shea Butter, Essential Oil, Fragrance Oil, Vegetable Oils, Food Grade

Question: is there a possible problem with excess KOH concentration?

 

I will recheck but it was definitely less than the initial, much as you found. First time there was a "psshhhh" sound, second time was just "ssshhhh" without the percussive start.

OK on your reasoning about the KOH concentration. I would be curious to know what the factory fill level and concentration is, but I doubt anyone is going to drill a new module to find out. Do new modules make a sloshing sound when shaken?

 

If water is evaporated slowly off the battery and KOH or whatever solute deposits on the inside wall in powder form, then I would just add pure water to re-dissolve the powder.

 

I remember when i charged/discharged all my modules to measure the capacity, the last one was about 4Ah i inputed charge to it over 9Ah(like in all other modules) at low rate charge 0.7Ah, then almost immediately started disassembling the modules from battery pack and that last module started little swelling and making little sound like "shhshhshh" .

At assembly process i shaken some modules and like i heard some sounds, but i did not pay much attention to it, now when will start the re-hydration process i will try again, i have 40 modules at different capacity, from 5Ah to 1Ah.

I wonder if the "valve unstick" procedure is necessarily during re-hydration process? i think maybe when the water will be injected it will wet the dried valve and will soften it and then it will open normally during operation in the car?

 

Roy from Canada here :

Thanks to strawbrad who referred us to a this post by Jeff K - this man did his experiment with boiling water and reported 2 years and 20000miles later, it reads as follows -----


"Hi Forumites! Recently I acquired a 2001 Prius for $1200. I own a 2008 and a couple of EV's so I figured I could bring this Prius back to being a usable daily driver. I was told by the previous owner that the car got a new battery not long ago. Be that as it may, I was soon finding out through codes that I had a few HV battery issues. First, there was one block giving code 3028. This means they are weak or some such. Armed with info from here, I tore into the pack.

I found it to be a 2007 replacement! I got a couple "good" modules from the Bay of E and installed them. The symptoms of fan blower coming on, brake light and racing engine occasionally went away and I was happy. But still the error lights came up! So I had the car scanned by a competent individual. The pack showed low capacity and to make matters worse, the block of two modules I replaced were WORSE than mine! But now I was really mad.

Why would the pack from 2007 (well after all the leaking KOH nonsense was sorted out) still fail in just a few years? My theory was heat because the car lived near Death Valley! What more brutal test of a battery, huh? So basically the moisture in the cells simply dries up. It happens in many battery chemistries.

Now I should say not only am I cheap--I am creative. I thought about putting in Gen 2 modules but thought matching the two from different cars would be a pain. I certainly did not want to spend actual money on a new pack or even a Re-Involt. My mileage was telling the story. The car could barely do 29MPG in the city!

I decided with nothing to lose, I would try reviving my pack. I looked over Bob and other's great info here and other places on the web and came up with my own approach which I now share here...

Because each module has 6 cells, I wanted to be able to attack them individually and not have to take the modules out or be baking them and stuff like that. Here is the basic method:

Small holes are drilled above each well. Boiling distilled water is injected via syringe--30ml each. The boiling water makes the grids or plates more likely to wick up some water. Panasonic used a gel originally but "re-gelling" them would be impossible...

Stainless steel screws are "self-threaded" right into the case after the water is insjected. I wanted to use some o-rings but got lazy. The screws can be opened in the future should you go to Death Valley once more. As Bob notes, The dissimilar plastic screw interface may leak vapors. But between the main vent opening and the fact that these batteries should not vent under normal conditions, I did not make any big deal over it. I did test melting chunks of a junk case into the holes with a simple soldering iron and it works great but is time consuming. May be the way to go if you are worried about leaks.

Now the real-world data: I have a battery analyzer and used it to come up with the water amount and test a few loose modules. As Bob notes, you need to do several charge discharge cycles to get capacity back. I started by seeing 2.5AH and in the end around 6AH before I decided things were going well and I started drilling holes in the modules of the car.
After the pack was rehydrated and I had been driving it around a bunch I found the mileage going back up to the normal Prius expected range. Today, I drove it about 10 miles city driving and it stayed at about 42.5MPG. I will update here with the ongoing results...

I invited the competent individual to scan the car again and repeat the battery tests. The HV battery now tests within usable range as far as capacity. ...For how long? That I don't know but things look great so far for my $4 screw investment and the gobs of time drilling and filling. Sadly, I still have an HV leak (not in the battery) that may be the dreaded MG2. I am resolved to grinning and driving with much better mileage and not looking at the error lights. I doubt I can stand that very long and soon will be drilling holes in the MG 2!

Jeff K."

He posted again 2 years later

"Thought someone would want to know... Car is still working fine, no codes, no issues (other than people like to crash into it!). Approximately 20,000 miles on rehydrated pack as of today! I'd say it worked. Jeff"


What do you think - he used 30 ml of water???

Gen 1 Battery Rehydrating Experiment Results | PriusChat

 

I suggest that what Jeff K meant was he used 30 ml per module. A careful reading of his post shows he did not specify 30 ml per cell or module.

I had some time today for experimenting and cut the top off a Gen I module. Then I used a digital scale to weigh the module dry, with the plates covered, cells full, and finally with the water shaken back out after the plates had 30 minutes to absorb what they could. The weight gain with the plates covered was 53 grams, full 75 grams, and just the plates absorbing what they could hold 9 grams. It is interesting that the absorbed weight gain matches the number mentioned in the patent. Even a dumb Merican can convert grams of water to ml. So I came up with 53 ml to cover the plates, 75 ml of total free air space, and the plates can absorb 9 ml. These numbers are in agreement with what you and others have measured.

I cut just the very top of the module off. I had to clean up and finish the cut with a file to reveal the inside of the module. I could not find the vent holes between the cells. I might have cut through them if they are at the very top of the cells. I can fill one cell full and it does not drain to the others. The module I opened had one bad cell that measured .06 volts. On a 6.5 amp charge it took just 27 seconds for that cell to reach 1.5 volts. So I learned something today. Watch for a rapid voltage rise in the first half minute of charging. That would be an indication of a dead cell with little capacity. I charged the module at 6.5 amps with just the 9 ml of water the plates held on to. The dead cell started to gas right away so added enough water to cover its plates. The bad cell bubbled away like a slow boil. The other cells started to gas at about 1.45 volts. It is cool to see inside a module charging. I stopped the charge at 3000 mAh. On discharge the bad cell had just 85 mAh before going in to reversal. I continued the discharge on the other 5 cells for about 2500 mAh. The 5 cells are now on a cycle charge and discharge for the night.

Brad

 

John,
I just measured the free air space capacity of a module at 53 ml to cover the plates and 75 ml to the top of the cells. Per cell this is 8.8 ml to cover the plates and 12.5 ml to the top. Roy measured 7.5 ml to cover the plates and 10.5 to close to the top. His last measurements where done after the plates had already absorbed what they could. Our results are close enough to be in agreement. John K did not put 30 ml of water into a cell with a capacity of 12.5 ml. He could have put 30 ml into a module or 5 ml per cell.

Brad

So I managed to NOT burn my garage down overnight. I always worry about leaving chargers unattended. I set the charger for nine cycles with a 6.5 amp charge, 1 mv delta peak per cell, 20 amp discharge to .9v per cell . This was done to just the 5 good cells. The dead cell I bypassed. The five good cells had just the tap water that the plates could absorb, 1.5 ml each. The dead cell was filled with tap water to the top and did not drain into the other cells. The last discharge shows 6091 mAh at a 20 amp discharge rate. Not too bad for a junk module.

I doubt the dead cell can be revived. Does anyone have any ideas of how to try to revive it?

Brad

 

The 6.5 amps was the charge rate. I did not monitor the cycles. Since the last charge was 6658 mAh at 6.5 amp rate the charge would have taken just over an hour. Slamming charge in at 6.5 amps and then immediately discharging at 20 amps 9 times is almost as abusive as cutting the top off the module. A high charge rate with the delta V set at 1mv per cell will tend to end the charge early.

The dud cell is not open circuit. I put the first 3000 mAh charge through all six cells. The dud just bubbled away most of the water over the plates.

When adding water to the dry cells I could see the plates quickly absorb and spread the water. Given a five minute soak completely covered the plates absorbed 7 grams of water. Then after a thirty minute soak they had absorbed 9 grams of water. I could also see the plates start to slowly bubble at about 1.45 volts. Durring the 3000 mAh charge the dud cell boiled off 3 to 4 ml of water. Someone smarter than me could calculate how much pressure that could build up.

Why can I leave just one cell full of water overnight and you can pour water through the module from one cell to the next?

Brad

 

Just a quick question John @Britprius,

Would you recommend rotating module positions from near the center of the pack to the ends and vice versa if one has refilled the electrolyte in all of the modules?

 

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