# Prius Batteries for EV



## IamIan (Mar 29, 2009)

if you get them from salvage yards they can be found cheap.

but you will have to cycle test them to make sure there aren't bad cells.

In the end ... they are not energy dense NiMH ... they are power dense NiMH ... different siblings in the NiMH family ... in short... power NiMH , like in Hybrids generally have the same energy density as Lead Acid ... 

they do have some operational benefits if you like them.

There are a variety of BMS design types for NiMH ... how hard you will be pushing them for discharge and charge will limit how cheap you can go without killing the batteries.

What kind of power and energy consumption rates and such does your application have?


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## jwr813472 (Jun 1, 2010)

Hi IamIan
Thanks for your post. I would be using the batteries in a VW with 8in series wound motor and a 500amp controller. I just re-did the math and I think I would end up having to remove the back seat and filling the void with batteries. Propably not worth the trouble of finding multiple packs that are close enough in age etc.


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## MN Driver (Sep 29, 2009)

Assuming that the capabilities of the Prius cells are similar to what is in the Insight. You can peak them at 100 amps for about 10 seconds, maybe 15 seconds if there will be a light load on them. ...with a 500amp controller, you only need 32.5Ah if you were only going for the peak rating but you'd need lots of cooling if you wanted to continue drawing from them.

These aren't ideal for an EV conversion IMO, especially recycled packs. NiMh can be a beast of a chemistry down the line when they wear out because their self-discharge is fairly high and as the cells age, the self-dishcharge gets worse, but it doesn't stay even amongst all the cells in the pack. These also don't like to be charged in parallel either because you don't terminate their charge based on voltage, but instead on negative delta voltage or delta temperature rise if you want a quick charge. Prius cells have very little -dV and people have reported their hobby charges blowing past charge termination and swelling the cells. Prismatic NiMh also don't like being too hot either so terminating based on temperature rise rates is going to lead to a short life too.

The first thing you need to do is create a matched pack where all the cells are very close to matching capacities, weeding out all the ones with high internal resistance, high self-discharge, and any other problem cells. You need to cycle the cells at least 3 times or so until their capacity increase is minimal to break them of their NiMh memory and then match up the cells with the closest capacity as you can. Once you have a good matched pack you need to charge them all full and then you can give them a low rate charge of about C/10 and charge them until the voltage settles for an hour or so. Then you can take that voltage and set that as your charging voltage maximum, use a current-limited supply set to that voltage and use that to charge them. ...but then you need to be able to time it properly so it stops on time to avoid overcharging them otherwise they swell up and develop tons of heat. Your best bet is to get the voltage at C/20 and when the cells are full, they are receiving a minimal amount of current. You don't want to parallel them because their voltage doesn't match the state of charge well and they all have different internal resistances, especially when they are recycled Prius cells.

These are tough to work with if you aren't doing something small. I've spent my time with Honda Insight sticks and have managed to get 5 good matched sticks out of a dozen. ...after sitting for a month though, I've got 2 of the 5 that are self discharged a bunch so I can never charge them as a pack at high currents otherwise I'll kill the ones that don't self-discharge. If I use them on at least a weekly basis I might get away with it if I put my temperature sensor on the cell that gets the hottest but that is less than ideal. I'm using mine for an ebike project(5 sticks of 6 cells) and if I can manage to get a Black and Decker 24 volt battery powered lawn mower for less than $50, I'll use 3 sticks(18 cells), or might bump it to 4 sticks(24 cells) which will probably be way too much to power the mower. I might parallel 3 sticks with a parallel matching set for the discharge but I won't charge them in parallel. Charging them like this is fairly wasteful too, their charge efficiency at low rates like C/10 is a factor of 1.6, you need to put in 60% more than you get out. I think the Prius packs and Insight packs are better than that but pretty much any site discussing NiMh's puts that number on them.

I don't think these are ideal, by the time you've cycled and matched up Prius packs, the whole EV battery mess will be taken care of and it will be clear who the affordable and credible Lithium suppliers are, in my humble speculation. These packs are heavy for their capacity and produce a fair amount of heat too. The Insight will charge them at 50 amps and discharge them at 100 amps but it doesn't take long to get them really hot with just 30 amps of discharge. I don't know about the Prius but from what I'm reading it only charges and discharges them at a very small range of about 10% and hangs right in the middle of the state of charge too.

I'm trying to point out the realities of the situation and rooting for you if you want to go for it but it will take quite a bit of effort. I see it making sense for the ebikers or in any use where you don't need to parallel cells but the bigger you try to make a pack, the tougher it will be. If we had affordable NiMh around in the capacity you need, I'd point you that way but it seems the very capable EV-95's are gone and I just don't have faith in the long-term life of used junkyard hybrid NiMh cells without quite a bit of maintainance to weed out cells that drop in capacity or self-discharge.


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## jwr813472 (Jun 1, 2010)

Thanks all,
You have convinced me that they are not worth the trouble. Now to save my pennies for TS or Sky Energy.


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## bigdawg7299 (Jun 8, 2010)

I was just researching the same thing. I found out that the Prius battery packs have changed over the production run of the car. Not sure if they all use the same 1.2v cell or not. I also found out that they are kept @40-60% charged to prolong the life span of the pack. Seems like way too much trouble to use.


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## Snakub (Sep 8, 2008)

Was anyone able to find a good means of charging prius packs since this post? I am thinking of putting together a drag bike with prius batteries. How many amps can they deliver beyond their c rate?


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## vpoppv (Jul 27, 2009)

Snakub said:


> Was anyone able to find a good means of charging prius packs since this post? I am thinking of putting together a drag bike with prius batteries. How many amps can they deliver beyond their c rate?


 The best source I have found so far for Prius module charging is on Endless Sphere. I have 33 modules and hope to some day find a use for them....

http://endless-sphere.com/forums/viewtopic.php?f=14&t=6726


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## bangerla (Dec 11, 2008)

Prius packs are very difficult to work with. Nimh is very hard to use in a parallel configuration, since the cells dont share current well. You also have to remember to keep the cells in compression, since they have very weak sides, and will burst. I bought 11 prius packs for converting a Ford ranger over to prius packs. In the end, I gave up, since it would have been quite difficult. Here were my thoughts on how to go it though:

Assemble 300v strings of prius batteries, and isolate each string from each other using a high current diode. This would prevent one string from discharging into another.

Place a relay on each string, and use a bms to match the string voltages. So as you are discharging the strings, disconnect the lowest voltage string until the rest of the strings reach the same voltage level.

You would need to do the same thing with charging as well. Or use a separate or switched charger to charge each string individually.


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## aeroscott (Jan 5, 2008)

bangerla , do you have one of the factory Ranger ev's. I have one that came with la 8 volts gels and was thinking the same thing .


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## bangerla (Dec 11, 2008)

I had a Ranger, but sold it in the gas crunch of 2008. The battery pack was bad on it, and EV prices were out of sight, so I figured it was a good time to sell. I am sure the prices on the Rangers will drop drastically in the next year, when all the new production evs are out.


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## aeroscott (Jan 5, 2008)

that's when I got mine a guy offered to me for 3k I didn't have any cash so cash advance @ 25% .


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## TexasCotton (Sep 18, 2008)

so no one cracked this yet on the charging of the prius nimh module


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## bangerla (Dec 11, 2008)

Frankly, with the current prices of Lithium batteries, dealing with the prius batteries is more trouble than its worth.


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## bangerla (Dec 11, 2008)

I never said that the batteries werent cheap. But to make them work you are going to spend a lot of money. If you want to run them to 100% they will need to be actively cooled. You will need a refrigeration cooling system to keep them from getting too hot. The batteries will also need to be run in separate strings, and you would need a controller that would keep them all balanced while you are drawing from them, and feeding power back to them in regen. I have charged hundreds of prius cells, and have bought many packs, and have learned that there is a reason Toyota only ran them from 20-80%. This was their way around the cooling problems and charging problems.


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## IamIan (Mar 29, 2009)

TexasCotton said:


> so no one cracked this yet on the charging of the prius nimh module


Just like any other 7.2V or 6 cell NiMH battery... it was 'cracked' decades ago... nothing much has changed about the charging process in that time.

The harder you push them the more important a good BMS is.
Harder meaning ... the C rates of charge and discharge ... as well as the % of used capacity.


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## TexasCotton (Sep 18, 2008)

Okay
Here is the thing I have read where people have charged the whole prius nimh battery pack. I have little or no idea with what or which charger. BMS is not an issue got that covered. The charger diy is hard .I have not seen or found a Nimh charger which covers 28 modules 7.2v 6.5ah 201 volt, I need slow charge with no more than 1-3amp............. heat can be overcome with fans


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## TexasCotton (Sep 18, 2008)

IamIan said:


> Just like any other 7.2V or 6 cell NiMH battery... it was 'cracked' decades ago... nothing much has changed about the charging process in that time.
> 
> The harder you push them the more important a good BMS is.
> Harder meaning ... the C rates of charge and discharge ... as well as the % of used capacity.


show me please the charger


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## bangerla (Dec 11, 2008)

google is your friend... Or go to batteryspace.com and buy a nimh charger


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## IamIan (Mar 29, 2009)

TexasCotton said:


> show me please the charger


Seriously? There are thousands if not millions of charges over the decades that charge NiMH batteries.

Honestly, I don't know how you could be aware of NiMH batteries and not be aware of the existence of chargers for them.??? 



TexasCotton said:


> Okay
> Here is the thing I have read where people have charged the whole prius nimh battery pack. I have little or no idea with what or which charger. BMS is not an issue got that covered. The charger diy is hard .I have not seen or found a Nimh charger which covers 28 modules 7.2v 6.5ah 201 volt, I need slow charge with no more than 1-3amp............. heat can be overcome with fans


The need for a BMS varies depending on the context ... I would not go so far as to say it is not an issue outright ... there are benefits of a BMS to any battery pack , of any chemistry ... BMS are not free so it becomes a scale ... and the question becomes ... are the BMS benefits good enough to warrant the BMS cost ... but there are always benefits to a BMS itself... some battery chemistries are more tolerant than others to the lack of a BMS , or a specific types of treatment ... and that tolerance can of course be a factor when one weighs pros and cons on the scale of to use a BMS or not.

There are a variety of methods of NiMH charging ... all are decades old ... nothing new for a long time ... some methods are more difficult to do than others are ... Trickle charging can be easier than Peak Voltage methods , or -dV methods , or dV/dt methods , or dT/dt methods , or CC methods , etc ... etc ... not all methods are equally difficult ... and they all have pros and cons ... they are not all equal to each other.

There are a vairety of methods to charge 168 cells ( 28 modules 6 cells each ) ... in an ideal case a properly designed BMS would control the charging on each individual cell ... but as written above , BMS are not free ... There are a variety of methods that can be used to charge the whole 168 cell pack as if it were one unit , and without a BMS for cell level control... some of those methods are better than others ... some are easier than others ... some are cheaper than others ... etc... etc...

You can build simple devices yourself if you like ... or if you educate yourself enough you can build complicated devices yourself ... or you can spend $ in order to pay someone else to do this work for you simple or complex ... there are a variety of choices... which one tips the scale the most in your case will of course vary by the priorities you have and what value you place on different things.

There are several devices you can buy that are able to apply a charge to the whole 168 cell battery pack ... and they are not all equal... which one best meets your individual preferences is up to you ... I would not presume to make a choice for you ... with more information about your criteria I might be able to offer some suggestions ... things that you would eventually be able to find on your own with your own search efforts ... I don't mind saving you a bit of search effort and time ... but I would need more information about your criteria in order to narrow down the multitude of options I currently see available to you.

Right now ... The Criteria I see you've presented so far is a 168 cell NiMH Battery Pack made of prius 7.2V modules you are looking to charge at a rate of 1 to 3 amps ... what other criteria do you have? ... do you care what it costs? .. do you care what NiMH charging methods it uses or doesn't use? ... etc ... etc.


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## TexasCotton (Sep 18, 2008)

Cost is not a factor but value is. I just want to match charger to the application. I will time my charger for safety (1-2hours max)as I seen blown up nimh modules and want to avoid at all cost. I do not mind the smart charger.I am tryin to get more of a charger system with failsafe... this is new to me.Yea battery space, all battery, and electrify all good stuff .


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## IamIan (Mar 29, 2009)

TexasCotton said:


> Cost is not a factor but value is. I just want to match charger to the application. I will like time my charger for safety (1-2hours max)as I seen blown up nimh modules and want to avoid at all cost. I do not mind the smart(dumb) charger setup.Trickle charge is good to. If I understand what method or how used and works I am not that admit to anything...If you can not tell this is new to me.Yea battery space, all battery, and electrify all good stuff . I just need match charger, bms, and battery pack


The safest method is not compatible with your listed 1 to 2 hour criteria.
Nor is a Trickle Charge ... A trickle charge takes more than 10+ hours.

1-2hours criteria is considered a fast charge rate ... and it is inherently harder on the battery cells than slower methods... but it can be done comparatively safely.

Before you go investing in a whole BMS for the 168 cells ... I'd recommend taking a hard look at exactly what you want to accomplish.

So tell me.
Why are you trying to charge the pack?
What is it you are ultimately hoping to get out of grid charging it?
What is the purpose?


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## TexasCotton (Sep 18, 2008)

Check out this forum thread http://priuschat.com/forums/prius-p...1-one-year-driving-our-bms-plug-in-prius.html


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## bangerla (Dec 11, 2008)

TexasCotton said:


> Okay
> heat can be overcome with fans


If you are running a large battery pack, and are in a warm climate, fans are not enough. The Nimh ford Ranger EV's would not charge if the ambient temp was over 90 degrees, because the pack would get too hot. On the S10 EV, they had a heat pump to either heat or cool the Nimh pack while charging. If you look at many of the large Nimh cells for EV's, they are liquid cooled. Research the Prius batteries, and you will see that they limit the charge to 80% to prevent the heat. They also installed the battery inside the car, to use the cool cabin air to cool the battery. Toyota assumed that you would always keep the inside of the car at a comfortable temperature, which would also be the right temp for the batteries. If you drive the Prius in 100 degree weather, with the windows down, and the AC off, then you defeat their engineering.


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## bangerla (Dec 11, 2008)

For a charger, you could use several Vicor flatpac power supplies in series, or a megapac with 48v modules. Then use the trim function on the power supplies to set the voltage for 80% charge. Vicor has an application note on their website on how to use the power supplies as a constant current / constant voltage charger.


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## IamIan (Mar 29, 2009)

bangerla said:


> Then use the trim function on the power supplies to set the voltage for 80% charge.


Not for NiMH... and not for a potentially unbalanced 168 cell pack.

NiMH SoC is not as closely predictable to a set voltage as some other battery chemistries.

Also in a potentially unbalanced pack ... without cell level BMS ... one cell out of the 168 cells +0.3v higher than the others would not be seen if another cell is -0.3V lower ... because you only see the voltage of the entire pack... 1.5v for one cell and 1.2v for another cell looks the same externally as if they were both 1.35v.

To use a voltage point approach you don't know what the SoC % is until you reach nearly full or nearly empty for all the cells in the pack together ... because some cells will reach 100% full before others are 90% full ... the charging current of such a system should be low enough to minimize the potential damage to the cells that reached 100% first and are beign slightly over charged.


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## IamIan (Mar 29, 2009)

TexasCotton said:


> Check out this forum thread http://priuschat.com/forums/prius-p...1-one-year-driving-our-bms-plug-in-prius.html


nice link.

Doesn't tell me what you want to accomplish though.


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## MN Driver (Sep 29, 2009)

If you understand how the Prius and Honda manage the NiMh, you'll understand that managing at the cell level is not required at all. Study up on how they work and you'll understand how you need to monitor the cells on discharge as there is no reason to monitor every cell to know that a cell is about to hit its fully discharged SOC level. You don't need to measure the 1.2v level to see a sudden near 1 volt drop out of a small group of cells that didn't happen to the rest at a given load.

You can actually use the same technique they use to monitor lithium cells too, in fact the batt bridge guys are doing it to the extreme by splitting the pack in half and doing it in an even simpler way. Not necessarily the way I'd do it for lithium and NiMh needs more attention than that, but I'll digress.


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## IamIan (Mar 29, 2009)

gottdi said:


> There is NO cell level you can check. You can only check each battery which has a total of 6 cells per battery. So you have battery level only. Lithium can do cell level. Not NiMH Prius batteries.


There is always a cell level that can be checked... anytime there are individual cells... Even if it is not easily accessible to do so... the type of battery chemistry has no impact on that ... the type of packaging of the cells however does effect how difficult it would be to do so ... so 6 NiMh cells or 6 Lithium cells packed the same way make no difference , it is just the packaging itself that effects the difficulty of accessing the individual cells.

I think , the better question is weather it is worth doing so ... and for some of the most common applications ... like correcting SoC on out of balance states ... Grid Charging ... etc ... there are options that can do a reasonably good job without going to a individual cell level BMS... that doesn't mean there aren't benefits to a individual cell level BMS ... or that is can't be done ... but just that I think the benefits come at too high of a price... at least for OEM Prius 6 cell NiMH Modules.


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## IamIan (Mar 29, 2009)

MN Driver said:


> You don't need to measure the 1.2v level to see a sudden near 1 volt drop out of a small group of cells that didn't happen to the rest at a given load.


While I will agree the method used is better than some alternatives ... I do still see benefits to a individual cell level BMS that are not all equally available without going to the individual cell level.

In your example ... by the time you see the near 1v drop in the total pack voltage the over discharge event has already happened for that individual cell that dropped out ... it is already rapidly heading toward if not already in voltage reversal ... the best the whole pack monitoring style system can do is try to minimize the amount of and the degree of impact from such events... Additionally while the OEM systems do a fair job ... but they are not perfect and they are not without potential for improvement.


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## TexasCotton (Sep 18, 2008)

I currently use SG2 SOC% and BTV


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## IamIan (Mar 29, 2009)

gottdi said:


> The Prius batteries don't offer a way to check at the cell level.


No OEM way ... yes.
however ... why limit to OEM methods?

Each of the 7.2V modules contains 6 cells... that are electrically connected in series inside the module.

It's the packaging... the chemistry used has nothing to do with how accessible individual cells are ... that is just the packaging of the modules.

I could take 6 of those lithium cells of yours and package them into a 6 cell module that conceals the series electrical connections just as much or more than the Prius NiMH modules do ... it is just the packaging ... there are always individual cells inside.

So like I said it is just a question of weather it is worth the cost / effort or not.



gottdi said:


> Are Prius batteries worth the trouble? In my book, NO.


In my book they are on par with ... slightly better than Lead Acid.

Depending on the specs of the application and how much they cost to get ... would determine if they are worth the trouble.

If you can get them cheap enough ... they can perform better than a lead acid pack could ... for some applications... but they are not a good fit for all applications... nor are they always found cheap enough.


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## TexasCotton (Sep 18, 2008)

Yes 
The design aka packag you have 6 gel cel nimh 1 module 7.2volt 28 module 201 volt--240vdc depend on SOC.
14 pos 14 neg going pos neg pos neg alternative with to copper buss bar
The complete 28 pack should not be charged beyond 80%(my application) If charged to 90%-99% you get more heat build the closer to 100% the more volatile gel cel becomes.
The charge cycle is more critical after reachin 80%-85% (my application) and better to not go beyond.

I have found where someone is using medical type equip to charge these. The equipment is called* electrophoresis*. I have also found electrophoresis power supply ......


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## MN Driver (Sep 29, 2009)

gottdi said:


> If a choice of Lead or Prius cells were the only choice I'd pick lead.


It depends on the application. If you need 6.5Ah or smaller cells where you don't need anything in parallel and would like to run deep discharges, lead wouldn't be a good choice.

To the poster trying to figure out how you are going to manage Prius cells, what is your application? Besides trying to figure out your charging and discharging scheme. What Ah capacity and voltage do you need. How deep are you discharging?

Without the application, these questions we are asking and the answers we are providing might be useless in comparison to how they might otherwise be helpful.

My application has no real monitoring at all because I will never run them empty and if I do, I really don't care. Let me explain. The cylindrical NiMh I am using can handle reverse voltage without croaking the first time it happens. Granted it's not good for it and will shorten its life dramatically but I've put these 6 cells series packs to the test running them to 0 volts repeatedly and pushing 2Ah backwards through a bad cell out of 6 and watched its voltage sit at -.2v or -.3v and generate enough heat to where you won't want to keep your hand on it. ...they still handled 50 cycles of this sort of abuse as a 6 cell battery. Granted the Prius prismatics might swell and become useless, I'm not sure but you can't do this with lead or lithium, they'll die or in the case of lead for sure but maybe lithium they will burst, nothing like getting the acid all over the place from a lead battery.

My application is 9 of these in series for 54 cells attached to an electric lawn mower, originally it was going to be for an electric bike but I scrapped that idea. I actually have 3 but don't use them because they have a few low capacity cells that I weeded out easily while testing them. The others give out over 6Ah. They are about 65v nominal but when I'm using them they are usually closer to 70v until they are at a low SOC. My moderate voltage pack doesn't need much Ah but if I built the same pack with lead and tried to get the same capacity I'd have to go with much larger than 7Ah lead cells and the whole pack would be unweildy and heavy due to the peukert at my 10-15 amp draw.


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## IamIan (Mar 29, 2009)

MN Driver said:


> Without the application, these questions we are asking and the answers we are providing might be useless in comparison to how they might otherwise be helpful.


Good Point.



MN Driver said:


> they still handled 50 cycles of this sort of abuse as a 6 cell battery. Granted the Prius prismatics might swell and become useless, I'm not sure but you can't do this with lead or lithium, they'll die or in the case of lead for sure but maybe lithium they will burst, nothing like getting the acid all over the place from a lead battery.


I think you hit the nail on the head ... I think a big factor in why cell level BMS are comparatively rare / unknown on NiMH packs ... even ones with hundreds of cells ... is at least partially because of the tolerance of the NiMH chemistry to abuse like that.

I mean due to the roughly 1/3 cell voltage it could likely be a more complicated and more expensive cell level BMS than a equal Li total battery pack voltage ... combine the increased complication and expense with the reduced benefit due to increased chemistry tolerance to abuse ... and it really isn't much of a surprise I guess.

I mean there are a fair number of people who don't think the added complexity and cost are worth the benefits even for some Li systems ... and those need fewer cell monitors in a less complicated system to manage a less tolerant chemistry.


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## rongsak (Sep 9, 2012)

i found some source : is possible to rebuild prius battery by you self . because my country battery is very expensive if is can may i save more money i pocket

link : http://tinyurl.com/Rebuild-Your-Prius-Battery


" hope is real story "


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## rmay635703 (Oct 23, 2008)

rongsak said:


> i found some source : is possible to rebuild prius battery by you self .
> 
> link : http://tinyurl.com/Rebuild-Your-Prius-Battery
> 
> ...


No shit Sherlock, but you don't need an ebook, although it does show you how to dissassemble it with pictures.

Many have refurbished prius & honda packs by doing intercell charging but once you start you can't stop or you need to take (2) packs and replace individual cells to make a good string.

Certainly nothing amazing about replacing cells or modules, you still likely will need good battery cells if you don't want to be using a grid charger everyday.

Cheers
Ryan


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## TexasCotton (Sep 18, 2008)

rongsak said:


> i found some source : is possible to rebuild prius battery by you self . because my country battery is very expensive if is can may i save more money i pocket
> 
> link : http://tinyurl.com/Rebuild-Your-Prius-Battery
> 
> ...


this has been on ebay and web and falls in line with the ebay rebuilders who want 1700 dollars and up for a unwarranted quote "rebuilt" hv battery ..........sorry gotta say a big fat NO to that.....


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