# 30% capacity loss after 4.5 years of driving



## corbin (Apr 6, 2010)

Hi all! I've been driving my electric bug for about 4.5 years. I just replaced a second "bad cell", which I know has lost about 30% capacity. This is after roughly 4.5 years, 39,000 miles, and charging once almost daily to 100% SOC (3.6v).

I'm using Thundersky Lithium iron phosphate cells. 48 cells, 200ah capacity, 3.2v nominal, for 154v nominal pack. ~30 kw/hr pack. 

Here's my blog post on it and some details:
http://www.corbinstreehouse.com/blog/2015/07/plug-bug-you-are-only-as-strong-as-your-weakest-cell/

I've *never* taken the cells to 20% SOC or lower. Really I have only done 30% a few times, and usually I would only take it to somewhere in the 40% range.

I really think charging them to 100% SOC was a bad idea. Instead, it would be much better to limit the charge to 90% to 95% SOC, keeping the cells at 3.2v and completely avoid the high voltage (3.5v and higher), except to occasionally top balance the cells or do a full 100% SOC charge for a long drive. 

-corbin


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## kennybobby (Aug 10, 2012)

Can you tell if the cell has vented, or does the cell swell up if you charge it on the bench?

Would you be able to do some full charge and discharge cycles to determine if it is normal wear loss of capacity or if it is an internal short that grew after an under voltage event?


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## piotrsko (Dec 9, 2007)

Hate to say it, BUT, you're within the realm of typical random failures. 4.5 years is perhaps 1,000 cycles on systems that weren't guaranteed to last that long.

Fwiw on electric forklifts at work, usually a new pack after about 2-3 years.

You are also acting as the lead participant in a capacity / duration experiment, so everything you've done at this time is one node of data for which is statistically erratic.

If it is published, look at the data for chevy, Nissan, VW, ET ALL and see what their failure fate is, categorized by type of failure. 

I think you're doing something right.

My $0.02, YMMV.


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## corbin (Apr 6, 2010)

kennybobby said:


> Can you tell if the cell has vented, or does the cell swell up if you charge it on the bench?
> 
> Would you be able to do some full charge and discharge cycles to determine if it is normal wear loss of capacity or if it is an internal short that grew after an under voltage event?


The cell has not swelled, and does not swell if charged; I did this experiment with my last cell that I had replaced.

Now, on the other hand, I say the cells do vent. How do I know? On hot days after the pack has fully charged and been sitting in the garage at work for 3-4 hours, I can smell it. It smells slightly sweet. This is when they are charged to about 3.6v (although some may hit 3.7).

This is definitely "normal" capacity loss, and not an internal short due to an under voltage event. I only drove the cell to less than 2.9 volts one single time, and that is it. It was at that point that I know what capacity it had left. It was also the cell that would always reach the top voltage first when charging.

I could potentially do bench charging tests...I might do it sometime, but I don't really have the right setup. My little RC charger only puts out 6 amps, and that would take 33 hours to charge if the full 200ah were available (and the charger stops every 5 ah, to make it more painful).

corbin


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## corbin (Apr 6, 2010)

piotrsko said:


> Hate to say it, BUT, you're within the realm of typical random failures. 4.5 years is perhaps 1,000 cycles on systems that weren't guaranteed to last that long.
> 
> Fwiw on electric forklifts at work, usually a new pack after about 2-3 years.
> 
> ...


Well...guaranteed to last that long is really only our DIY communities opinion on them (which is pretty accurate!). 

Thunder sky said (in their data sheet) they were good for 3000-5000 cycles to 20% SOC, and at that point should have 80% the original capacity. They never stated anything at the top voltage, and how long you should keep it there. Of course, when I go the cells they also recommended charging to 4.0 or 4.1 volts on the data sheet! We all know that is the worst thing for them. (NOTE: I did do this for a few months before rolling it down).

Model S batteries tend to not loose capacity...and I think it is because they typically avoid high voltages and full SOC. Whereas the 100-mile range cars (Leaf) tend to loose range because everyone almost always charges them to 100%.

corbin


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## corbin (Apr 6, 2010)

Also, here's a post on my other cell:

http://www.corbinstreehouse.com/blog/2012/12/plug-bug-bad-cell/

I think it had also lost about 20-30% capacity, and this was a few years ago. I lost my data on it (although I still have the cell sitting around).

Also, notice *slight* bulging of the package...but then gain, when I got the cells new the exterior was never quite flat.

corbin


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## Hollie Maea (Dec 9, 2009)

The worst thing for cell health (apart from things that destroy them immediately like reversing) is being hot and full SOC simultaneously.


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## corbin (Apr 6, 2010)

Hollie Maea said:


> The worst thing for cell health (apart from things that destroy them immediately like reversing) is being hot and full SOC simultaneously.


Yes, of course! Unfortunately, a lot of the "stupid" chargers (i.e.: Manzanita), don't have any way of counting amp-hours and stopping a charge at a specific SOC (sure, you could use the timer function..but it is horrid). So, the only option is to charge to 100%.

corbin


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## Moltenmetal (Mar 20, 2014)

Thanks so much for posting your experience and data.

I agree that charging to 100% SOC is a bad idea, and so is top balancing- very bad idea for very little benefit.

My charger has no means to stop at a certain % SOC- you can fake your way there by stopping at a lower total pack voltage, which is what people who bottom balance end up doing. Right now I have my BMS trip the charger when that one cell low capacity cell hits HVC at 3.68 V, but I bet I'll be there with a dead cell just like you in a year or two. Better get one, or two, on order now...!

Hot and high SOC simultaneously is worst, but tough to avoid if you need to charge to drive home from work in summer. There is some magic soup in the electrolyte mixture which helps to delay the inevitable oxidative damage, but there is a limited amount of it sealed into each batch of electrolyte. When it's used up, it's gone.

I experience the same sweet smell with my Sinopoly cells- diethyl/dimethyl carbonate presumably, which are both liquids at room temperature, added to the main electrolyte solvent ethylene carbonate which is a solid until about 35 C. Only a trace, and only noticeable from the rear pack which is well enclosed in my car. Never correlated it with high or low SOC.


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## nimblemotors (Oct 1, 2010)

You can just lower the charge voltage which leaves it less than 100% full, but does increase charge time. If you need full batteries for your commute, not much choice. You can add more cells so you don't need full charge.
5 years daily driving isn't horrible.
Is it just a few cells that lost capacity?
They should not be venting, that is/was a big issue, losing the electrolyte will surely kill them eventually.



corbin said:


> Yes, of course! Unfortunately, a lot of the "stupid" chargers (i.e.: Manzanita), don't have any way of counting amp-hours and stopping a charge at a specific SOC (sure, you could use the timer function..but it is horrid). So, the only option is to charge to 100%.
> 
> corbin


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## corbin (Apr 6, 2010)

Moltenmetal said:


> Thanks so much for posting your experience and data.
> 
> I agree that charging to 100% SOC is a bad idea, and so is top balancing- very bad idea for very little benefit.
> 
> ...


IMHO, I think top balancing is still a good thing. But my thread here isn't really about that topic. 

corbin


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## corbin (Apr 6, 2010)

nimblemotors said:


> You can just lower the charge voltage which leaves it less than 100% full, but does increase charge time. If you need full batteries for your commute, not much choice. You can add more cells so you don't need full charge.
> 5 years daily driving isn't horrible.
> Is it just a few cells that lost capacity?
> They should not be venting, that is/was a big issue, losing the electrolyte will surely kill them eventually.


Just lowering your charge voltage isn't really that easy of a thing to do with a PFC30, which seems to be affected by ambient temperature. Setting the BMS to stop the charge at a lower voltage is possible (say 3.5v instead of 3.4v), but I don't want to do that. 

I *could* write software to do this by reading the CAN bus from the BMS, checking the SOC, and stop the charging early; I know how, it just takes time. I just don't care to do it. If I was starting new, I would definitely do this.

Like I mention in my post, I'm not sure what other cells have lost capacity; the pack is only as strong as the weakest cell, and I haven't done any capacity tests since I've replaced the bad cell.

They should not be venting -- yeah, I agree, but I do smell something from them, so they are! I don't physically see any liquid or anything actually coming out of them. So, it also depends on what you mean by venting. 

corbin


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## corbin (Apr 6, 2010)

scott glen said:


> Hey Corbin, don't blame yourself, LifePO4 is junk compared to Li-ion Cobalt. I learned the hard way. After selling the "NEW" Volt and Leaf cells for over2 years, I have NOT had a single customer complain about losing a cell or having a weak cell. How many American car manufacturers use Chinese Phosphate, a big 0. Of course you will now hear form the cheapies still using lead that I don't know what I am talking about. Since I designed the first battery pack using 8500 18650 cells for a 70 VW in 2004,then selling it to T____, I must be on the right track.


Oh, I'm not blaming myself! I followed the manufactured specifications; I blame them. But I would do it differently if I were to do it again today. I don't know if I would use the square prismatic cells again; I'd research what to do based on what I wanted (performance, distance, etc). But if I did use them, I'd write custom software.

Note that people still see capacity loss in Leafs.

Also, my cells were fine for 3 years, so 2 years may not be long enough for people to complain. It would be interesting to know who is using Leaf packs, and for how long (both miles and time), and what capacity they are still out.

corbin


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## dougingraham (Jul 26, 2011)

It isn't clear to me that you have lost 30% capacity on all your cells but you may have lost more capacity on selected cells. Probably the weakest cells when they were new. In my car I tested every cell when they were new so I know exactly what the capacity was. Since I bought a few extras I did not use the 8 weakest cells.

Last year I re-bottom balanced the pack to see if there was any drift. I took that opportunity to test what was originally the weakest cell in the pack. Because I bottom balance this is the cell that reaches 3.5 volts first and the pack voltage where that cell reaches 3.5 volts is where I stop the charge. So I fully expect that cell to be the first one to wear out. As it so happens when I re balanced the pack I retested this cell and found that it had lost about 9 percent of its original capacity. This would be about 3% per calendar year which does not seem excessive. I don't drive nearly as many miles as you do so there are lots of variables.


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## corbin (Apr 6, 2010)

dougingraham said:


> It isn't clear to me that you have lost 30% capacity on all your cells but you may have lost more capacity on selected cells. Probably the weakest cells when they were new. In my car I tested every cell when they were new so I know exactly what the capacity was. Since I bought a few extras I did not use the 8 weakest cells.


Yeah, my post wasn't quite clear: it is 30% loss in one cell. I don't know about the others. I'd have to drain each one individually and count amp-hours...and I don't have a way of doing that. 

Your loss of capacity is more of what I was expecting.

corbin


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## samwichse (Jan 28, 2012)

How is the average capacity in the rest of the cells holding up?


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## corbin (Apr 6, 2010)

samwichse said:


> How is the average capacity in the rest of the cells holding up?


I think you missed my answer on that part, but the short answer is "I don't know". I haven't done a whole pack capacity test with the replaced cell, nor single cell testing. 

corbin


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## major (Apr 4, 2008)

scott glen said:


> Hey Corbin, don't blame yourself, LifePO4 is junk compared to Li-ion Cobalt. I learned the hard way. After selling the "NEW" Volt and Leaf cells for over2 years, I have NOT had a single customer complain about losing a cell or having a weak cell. How many American car manufacturers use Chinese Phosphate, a big 0. Of course you will now hear form the cheapies still using lead that I don't know what I am talking about. Since I designed the first battery pack using 8500 18650 cells for a 70 VW in 2004,then selling it to T____, I must be on the right track.





scott glen said:


> ...I designed the first battery pack using 8500 18650 cells for a 70 VW in 2004,then selling it to T____, I must be on the right track.


Where have I heard that before? Oh yeah! Exactly the same thing cruisin always claimed. 

Hey scott glen. Are you cruisin aka Alan Bullock with a new user name?


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## onegreenev (May 18, 2012)

> I will pass your remarks to Al when he gets back from Norway, working with Tesla.


What a load of crap. Bullock working for Tesla. Ha!

As for Leaf Cells being better. Thats a load as well. For the first couple years, sure. But they do loose capacity. Mine lost upwards of 28% after 36,000 miles. Still in Nissan's expected life. So that is looking to be the expected loss. I'd like to hear about Tesla capacity loss after those kind of miles. Id bet my paycheck that they too are close. 
2011/2012/2013 Leaf Cells drop some serious capacity at around the 36,000 mile range too. We shall see on the new Lizard Leaf Packs. Im not expecting much better. Hoping but not expecting.


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## Moltenmetal (Mar 20, 2014)

corbin: you imply the number of charge cycles, but didn't give a count. How many cycles are you at now?


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## major (Apr 4, 2008)

scott glen said:


> No but you best hide, Curtis has a piece of paper for you, looks like court order. A couple of others who provided information for illegal downloads, settled out of court. Your turn next. I will pass your remarks to Al when he gets back from Norway, working with Tesla.


There is not much truth in that post, Al, if any. But there is libel. So perhaps it is you who should hide.


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## rochesterricer (Jan 5, 2011)

onegreenev said:


> What a load of crap. Bullock working for Tesla. Ha!
> 
> As for Leaf Cells being better. Thats a load as well. For the first couple years, sure. But they do loose capacity. Mine lost upwards of 28% after 36,000 miles. Still in Nissan's expected life. So that is looking to be the expected loss. *I'd like to hear about Tesla capacity loss after those kind of miles. Id bet my paycheck that they too are close. *
> 2011/2012/2013 Leaf Cells drop some serious capacity at around the 36,000 mile range too. We shall see on the new Lizard Leaf Packs. Im not expecting much better. Hoping but not expecting.


You can do what you like with your hard-earned, but I wouldn't put down real money on that bet if I were you.

http://www.greencarreports.com/news...ow-much-range-loss-for-electric-car-over-time


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## onegreenev (May 18, 2012)

rochesterricer said:


> You can do what you like with your hard-earned, but I wouldn't put down real money on that bet if I were you.
> 
> http://www.greencarreports.com/news...ow-much-range-loss-for-electric-car-over-time


Predictions are one thing. Actual figures tell all. The benefit Tesla has is only because it has such a large capacity to begin with. It is hit pretty soft compared to packs of smaller capacity. Do a comparison of similar capacity packs of the different types of batteries. It could be Im wrong but you so far the results show a pretty decent capacity loss after 36,000 miles from packs of 24kW or less. 

Im hoping for better this time around. If not, Im out of the EV game and I'll go back to Diesel and BioDiesel fuels and for Gas cars, Renewable Alcohol fuels.


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## Hollie Maea (Dec 9, 2009)

onegreenev said:


> The benefit Tesla has is only because it has such a large capacity to begin with.


Yeah, that's not true at all. Cooled NCA vs uncooled Spinel? Huge difference.


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## rochesterricer (Jan 5, 2011)

onegreenev said:


> Predictions are one thing. Actual figures tell all. The benefit Tesla has is only because it has such a large capacity to begin with. It is hit pretty soft compared to packs of smaller capacity. Do a comparison of similar capacity packs of the different types of batteries. It could be Im wrong but you so far the results show a pretty decent capacity loss after 36,000 miles from packs of 24kW or less.
> 
> Im hoping for better this time around. If not, Im out of the EV game and I'll go back to Diesel and BioDiesel fuels and for Gas cars, Renewable Alcohol fuels.


The primary advantage of the Tesla packs is temperature control, not size. Most of the degradation I've seen in Leaf packs has been in very warm climates. I know many Leaf owners up here, and they haven't seen near that amount of capacity loss. You are certainly free to make whatever bets you wish, but caveat aleator.


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## tomofreno (Mar 3, 2009)

Hi Corbin,

I wouldn't sweat one bad cell. Thanks for the data. Here's some more:

20.7kWh pack, 180Ah CALB SE, top balanced, minibms, bit over 43,000 miles and 5 1/2 years, 982 charge/discharge cycles, no noticeable loss 
in range. There may well be some loss, but a few days ago I did the test I've described before: discharge pack to 30% SoC, pull 500 - 550A and see if the minibms LVC alarm sounds (@ 25C it triggers if a cell is at 2.6V for 4 seconds.). No alarm, so can't have lost too much range, certainly not 20%. 

I did mostly full charges for ~ first 2 years using a Manzanita PFC30. Partial charges roughly 60 - 70% of the time after that. Using EMW charger last 2 years, full charge is set to 3.55V CC/CV transition, CV to 0.05C at 0.5C charge current per CALB spec (these are all user selectable in the EMW). Shunts come on at 3.5V +/- 0.2V. All are on by end of full charge. Pack usually gets to around 115F 10 - 20 times per year in hot summer months, below 95F most of the time. Heated to 65F in winter.

I did swell one cell this January, but that was due to a brain lapse. I had bypassed the rear box of 8 cells with the bms chain while I was doing some work, then forgot to hook them back in. Over-charged what had been the high V cell for years. Bought another from Keegan, hooked those bms boards back in the loop, all good.

Here are some comments from a CALB representative I received recently:

_Cycle life specification is cycling cells at room temperature [~25 deg C] at 0.3C charge/discharge rate.

Operating cells at high temperature above 40 C will increase the capacity lost, the cycle life will lower than 2000 times. 

The cycle life in temperature below 40 C is about 40-50% more than that in 55C. 

There is no obvious difference between CA cells and SE cells on temperature performance._


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## onegreenev (May 18, 2012)

> Cooled NCA vs uncooled Spinel? Huge difference.


If the NEED of water cooling were as serious as you make it sound then all the EV's built, including the DIY ones we build, would have water cooling integrated. No. Its not as much of a deal as you state. The leaf does have a battery temp gauge that keeps track of the internal temps of the modules. To date, including the 2011 Leaf I purchased I have NEVER EVER seen my Temp gauge in the DANGER Zone. EVER and it does get hot out here. I plug in my car upon my drive home and even with that extra heat from charging NEVER EVER pushed the temp in a danger zone. EVER. The Leaf does not even have an air cooled pack. Its only by natural dissipation of the heat that it keeps its cool. 

The Water Cooling of the TESLA is not really much of a cooling system but it is there to keep the pack from over heating due excessive speed driving. It has some tubing around the packs of cells. The water cooling is not like the pack has all the cells immersed in water for cooling. No, just some tubing or channels to track some water through for minimal cooling to help keep the pack within temp ranges. 

The Leaf had its electrolyte changed to help combat the degradation of the internal components without the need for minimal water cooling to help. 

I see the Leaf does just fine. The issue was within the cell and not because of the heat. There is a danger zone but so far I know of no one that has ever had their battery temp gauge go into the danger zone. 

The other Gal at my work that still has her 2011 Leaf had to start charging at work via her super slow charger in order for her to get home. Her degradation is equal to the 2011 Leaf I had. She can't drive 45 miles after 4 years. I could not drive that far either. Performance had been good. Just capacity crapped out. 

We now have chargers at work. Actually 60amp 240 outlets to use with adapters. So all the Tesla owners and Leaf Owners can charge at work.


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## Moltenmetal (Mar 20, 2014)

If what I read is correct, Tesla's battery warranty does not provide a specific warranty against capacity loss. There has to be meaningful capacity loss over the 8 year warranty period. How much? With a pack that large, and reasonable driving expectations, does it really matter?!


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## piotrsko (Dec 9, 2007)

And fwiw: on my chevy pack I never see more than 10 degree temp rise even after dumping a whole charge into a 5 mile ride. Somebody said 145 watts knto heat. Kinda negligible.


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## Hollie Maea (Dec 9, 2009)

onegreenev said:


> If the NEED of water cooling were as serious as you make it sound then all the EV's built, including the DIY ones we build, would have water cooling integrated. No. Its not as much of a deal as you state. The leaf does have a battery temp gauge that keeps track of the internal temps of the modules. To date, including the 2011 Leaf I purchased I have NEVER EVER seen my Temp gauge in the DANGER Zone. EVER and it does get hot out here. I plug in my car upon my drive home and even with that extra heat from charging NEVER EVER pushed the temp in a danger zone. EVER. The Leaf does not even have an air cooled pack. Its only by natural dissipation of the heat that it keeps its cool.
> 
> The Water Cooling of the TESLA is not really much of a cooling system but it is there to keep the pack from over heating due excessive speed driving. It has some tubing around the packs of cells. The water cooling is not like the pack has all the cells immersed in water for cooling. No, just some tubing or channels to track some water through for minimal cooling to help keep the pack within temp ranges.
> 
> ...


Your circular arguments make my head spin: Leaf cells suck, so all the other cells must suck too BUT anything other manufacturers are doing differently must not be important since Nissan isn't doing it?

Look, it's nice that Nissan doesn't say that their cells are in the danger zone for temperature. Doesn't mean much when you have packs with 30,000 miles on them at 70 percent State of Health. Obviously, they are doing something wrong.

As you should know, different chemistries have different levels of sensitivity to overheating. Nissan's gen 1 cells, with a Spinel chemistry, are very sensitive to heat. Combine that with a pack that isn't even air cooled and you have the recipe for being notoriously short lived. Why you would extend that to other manufacturers is beyond me. The NCA chemistry that Tesla uses is less sensitive to heat AND they cool them. A bet that their life cycles would be similar to gen 1 Leat would be ill advised.

The LiFePO4 cells that most hobbyists use are even less sensitive to heat due to their lower voltage. Even then, cooling would help if there were a decent way to cool plastic prismatics.


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## MaxB (May 23, 2014)

Where are the Lithium Titanate cells? What happened with those? Does anyone know? Thanks.


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## rochesterricer (Jan 5, 2011)

onegreenev said:


> If the NEED of water cooling were as serious as you make it sound then all the EV's built, including the DIY ones we build, would have water cooling integrated. No. Its not as much of a deal as you state. The leaf does have a battery temp gauge that keeps track of the internal temps of the modules. To date, including the 2011 Leaf I purchased I have NEVER EVER seen my Temp gauge in the DANGER Zone. EVER and it does get hot out here. I plug in my car upon my drive home and even with that extra heat from charging NEVER EVER pushed the temp in a danger zone. EVER. The Leaf does not even have an air cooled pack. Its only by natural dissipation of the heat that it keeps its cool.
> 
> The Water Cooling of the TESLA is not really much of a cooling system but it is there to keep the pack from over heating due excessive speed driving. It has some tubing around the packs of cells. The water cooling is not like the pack has all the cells immersed in water for cooling. No, just some tubing or channels to track some water through for minimal cooling to help keep the pack within temp ranges.
> 
> ...


Given the MUCH higher instances of capacity loss for Leaf drives in hotter climates, I wouldn't put much stock in that "danger zone" gauge. Unless you like listing to the Top Gun soundtrack while you drive


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## Sunking (Aug 10, 2009)

corbin said:


> I really think charging them to 100% SOC was a bad idea.


Agree and so do all commercial EV manufactures as they mostly run between the sheets of 20/80. Once you go above 90 to 95% you start to do damage especially if held at that range or higher for any length of time. 

Personally I bottom balance and never have to worry about being over or undercharged. The problem with most Top Balance system using Vampire or Bleeder boards is they are set at or near 100% SOC. That is a problem. A solution is to be able to set the voltage to say 85% and communicate with the charger to cut back current when the first Vampire Board triggers so charge current can be limited to Bypass pass current to finish the rest of the cells without over charging the other slower cells.


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