Replace 1 cell in HV pack?

The success rate of single module (each module has six cells) replacement is low. The failing battery gets very hot which requires frequent stops to cool off but within the battery pack, the heat 'cooks' the adjacent modules which in turn fails them.

Now the 38 modules are in pairs numbered 1-19 starting with P3011, the pair closest to the control electronics. So P3014 means the 4th pair, two modules. But the next lower pair and higher pair have been exposed to the heat from the failing module. Worse, the 38 modules are built so well balanced that like the "Bishop's One Horse Shay," they run until they are almost all ready to fail.

Another part of the failure mechanism is heat causes the "O" rings around one the terminals to 'melt' and this leads to the loss of water and a little bit of the KOH electrolyte. This electrolyte 'eats' the copper buss bars that connect the modules together. Cleaning and neutralizing with a weak acid helps but the voltage sense lines can lose so much copper they break when handled leading to another battery fault.

Imagine you have an four cylinder engine and one cylinder has a failed valve. Trying to repair one cylinder alone takes as much work as repairing the valves of all cylinders. That is what traction battery repair entails.

Now you can do the work yourself if:

• takes typically a couple of weeks - this is the time it takes to survey the replacement modules and balance their 38 charges. The survey does a charge/discharge cycle to measure their capacity and then bring them to a consistent state of charge (SOC).
• alternate transportation while doing the work - many of us work and still need to shop and do the other things of life
• a smart charger that knows NiMH, six-cell batteries - the RC community has them. My MRC-989 cost $125 five years ago.
• parts - the original NHW11 modules were good but have relatively weak terminals. So most of us recommend getting modules from salvage cars or from resellers. If doing a module repair, you'll still need to test them before assembling the pack, the first step. Also, you'll either rework the buss bars or buy new.

There are a small number of pack rebuilders but these packs weight about 90 lbs and shipping is . . . a challenge. I've used ReInvolt of Summit NC but there are others around the country. Search the forum for recommended sources.

GOOD LUCK!
Bob Wilson

 

If you choose to replace only the bad modules ,at the minimum I would replace the 2 modules. It can get very time consuming to replace just the ones that fail,as you will be doing again sometime in the near future.. Nobody really knows how long that will last. At best its just a temporary get by fix..With that being said it can be done ,but remember BE SAFE!! and work carefully as this is not a job for the beginner.. Dont know where you fall in that catagory but just be careful..

 

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I just had the same problem
First let me say that after spending Many hours reviewing the different options I learned a few things.
1. the car knows it has battery problems and has gone into temp service mode, the frequent stops are a warning signal and the car is counting the temp emergency miles it is allowing you to drive, and Will shut down completely after a unspecified number of miles.
2. If you park the car for any length of time (more than a month) disconnect the small car battery, or use a trickle charger or it may be drained/dead.
3. get your transmission flushed/cleaned, that is the second most common expensive part to need replacing in the post 100.000 mile range.
4. I was unable to find a local shop willing to preform the recharge process due to High Voltage Concerns.

5. The $10 6 page how to r+r the battery book on ebay was worth it.

Now to answer your questions - It is possible to change the bad cells, yes that is a plural cells research showed that the average prius needed 3/4 cells replaced, (mine needed 3). (at $35. each average ebay cost)
The problem with that is that after getting the new used cells they Must be balanced with the other cells in the batt pac as mentioned above, and that is a long process. (Charge / discharge full set of 38 as a set 3 times, 3-4 days ea. cycle).
This might seem like a good low cost fix solution. But could mean that in 1 year you may be in the same boat. And no I never did find any posts about how long a reconditioned battery might last. It seems that a light vehicle use battery may last longer (mine at 140.000 mi.) so if you don't take long trips reconditioning may work.
Also as noted above your battery set is 10+ years old and even tho they really want to sell you those "reconditioned" battery units they are also of the same age, and ALL they do is Recharge them and slap a 6 mo warranty on them.
To me 6 months means 6000-10.000 miles. so you might expect 12.000 to 20.000 on a refurbished battery.
(caution if they want a core back you don't want to over pay for a simple recharge job some places want $1000).
If you do the work yourself this might sound like the cheap way to get by (7 hours r+r out+in), but one should know that the battery pak CELLS are bolted from the BOTTOM and requires removing it from the car to get them out, so if you think you may be back into those cells soon you might look into an alternate means of securing the system upon reinstallation (DANGER HIGH VOLTAGE LOCKOUTS POSS BYPASSED). if this is possible, one could just keep "recharging / rebalancing the batt pac system. on a recurring basis by simply removing the back seat and battery cover.
When it came to high voltage cautions 12v x 38 pacs = ? , and a 7 hour r+r I chose to replace the whole pac.
My recommendation is to park the car and save up the money for a new battery pak, I chose to install 2010 gen3 battery cells (they do work good) and are available on ebay pre ballanced. (cells need all 38, or full batt pac set ) for 3/4 the cost of Toyotas recommended new gen1 battery pac set. before installation.
For under $2.000 a mechanic friend and I replaced the cells and ive been on the road with no problems for 3 months now

The name of the ebay seller that had the gen3 battery cells where I bought mine was Hybrid.parts
or there real world name was
HYBRID AUTO CENTER LLC
(702) 374-8692
4350 Arville St, Bldg C #25, Las Vegas, NV 89103
yea I researched them too before spending that kind of money.

Hope this helped Minotor

 

You are getting cells and modules mixed up. The modules will cost you $50 each so two modules will cost $100 not 12 x $50 as in your post. One module consists of 6 cells that cannot be separated out.

John (Britprius)

 

If you are replacing only two modules regardless of the condition of any others that may show as being week during balancing, you will be doing it all over again in a short while.
If you replace any week modules your car may continue for a long period, but how long is any ones guess.
I have no experience of rebuilt batteries from manufacturers of such units but a rebuilt gen1 with gen1 modules does not sound a good deal at $1000. If rebuilt with gen3 modules even $1500 would be a good deal.
When you balance charge the modules the charger measures any improvement in the modules and records the capacity of the models allowing you to choose modules with similar capacity, typically around 5 amp hours (AH).
Using one module with a capacity of say 3 AH with all the others at around 5 AH will quickly discharge that module to zero then reverse charge it destroying it.

I also to an extent disagree with a previous post in that using the car for short runs will make it last longer. When the Prius is started from cold the battery is used to a large degree to keep load off the cold engine to reduce emissions. On a long run this does not happen the system does it's best to keep the battery at a steady level of charge rather than running it to it's bottom limits of discharge.

John (Britprius)

 

The modules are all in series. Your battery is only as good as your weakest module, and if they are all not of similar capacity and internal resistance the car will code. Then you get to do it again.

If you have the time to tinker you'll get lots of experience removing the battery/modules and reassembling everything.