# how do tesla batteries work?



## arklan (Dec 10, 2012)

so iv been googling the panasonic/lg batteries used in teslas.
the batteries have a max of 2c and have about 500 cycles.

lets say the tesla operates on 150v
if they have a 500ah pack thats a 75kwh battery pack which is about what the entry level one has i think.
thats 150kw or 225hp at peak but the wiki says it has 270kw/362hp peak so whats the story here?

if the packs are made from 18650s with 3.7v 3.4ah then it would take about 5960 cells and weigh about 275kg

pretty sure tesla works on 400v (108s 55p) thats still 150kw peak


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## brian_ (Feb 7, 2017)

Actual numbers would help your understanding. From memory...

all Model S/X batteries consist of 16 modules, each 6s (so 96 in series for the entire battery, not 108) - that's 355 V @ 3.7V, not 150 V
all of these modules are the same external size, but contain different number of cells in parallel at the lowest level

From a Gas2 article:


> In the company’s 85 and 90 kWh batteries, there are 16 battery packs containing 444 cells each. For its 100 kWh batteries, Tesla reconfigured the cooling system so it could fit 516 cells into each of the 16 packs for a total of 8,256 cells.


That's 6s74p per module for the smaller batteries (total 7,104 cells), and 6s86p per module for the 100 kWh (total 8,256 cells).

Any of the several forum members who have worked directly with Tesla modules can correct any errors above (please ).

If the cell maximum discharge rate were really 2C, then the maximum power would be 200 kW for a 100 kWh pack; clearly more than 2C is allowed, at least for a short duration.


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## brian_ (Feb 7, 2017)

With the Model 3 now dribbling into production, references to "Tesla" batteries, modules, and cells will need to be more specific.

The Model 3 uses larger cells (2170 format), and so fewer in parallel (but the same number in series) for a given capacity. It also groups the cells into fewer modules (only 4)

50 kWh: 96s31p for a total of 2,976 cells
74 kWh: 96s44p for a total of 4,416 cells
(information from electrek article)

Still, with 74 kWh in the larger battery and a 258 hp (192 kW) motor, the peak discharge rate must be more than 2C.


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## arklan (Dec 10, 2012)

*Still, with 74 kWh in the larger battery and a 258 hp (192 kW) motor, the peak discharge rate must be more than 2C.

*yeah it has to be! but all the info i can find on 18650s says they have 2c discharge so tesla must be getting some special version.
also the 18650s are meant to have 500 cycles only, and have to be stored at half charged, neither of which would be any good for a car.


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## Karter2 (Nov 17, 2011)

arklan said:


> *Still, with 74 kWh in the larger battery and a 258 hp (192 kW) motor, the peak discharge rate must be more than 2C.
> 
> *yeah it has to be! but all the info i can find on 18650s says they have 2c discharge so tesla must be getting some special version.
> also the 18650s are meant to have 500 cycles only, and have to be stored at half charged, neither of which would be any good for a car.


Look harder... there are many different types of 18650 cells with discharge ratings as high as 20C if that is needed, so forget the 2c generic figure you dug up from google. Understand the difference between "continuous" ratings , and "burst" or "pulse" ratings for discharge.
And cell life cycles depend on many parameters.
But Tesla doesnt use commercially available cells, they have their own specification custom made by Panasonic (but very similar to the 18650 BE spec)
And employ sophisicated charge and control systems to manage the cell usage.
The "proof is in the pudding"... Tesla give a 8 year warranty on the battery and there are plenty of reports to verify the power output and long life of these batteries.


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## brian_ (Feb 7, 2017)

As already explained, there are many "18650" cells, with substantial differences in internal construction and materials. That designation really just means a lithium cell 18 mm in diameter and 65.0 mm long, so you'll find lots of information about 18650 cells which does not apply to a specific vehicle using that size of cell.

I have some flashlights with 18650 cells; stated capacity varies between them, and I'm sure none of them match Tesla specs for anything (capacity, charge rate, discharge rate...).


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## rpsinghsethi (Jan 10, 2018)

All batteries work differently because the functionality differs from KW to Current and Mah to KWh. So, Inverter batteries, Car batteries and other batteries work differently. Tesla batteries have their own functionality. But, I have used Energy and Fire's batteries which are quite genuine.


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## efeballi (Jan 15, 2018)

AFAIK the early Model S'es used Panasonic NCR18650B batteries. They do have a max discharge rate of 2C on Panasonic's spec sheet. I've always thought Tesla has ~50% DoD on the batteries so can afford to pull higher power when necessary. 
With 50% DoD, the (stated) 100 kWh pack actually has a 200 kWh cap, with 2C discharge it can supply 400 kW.
If the numbers above are correct, this is not the case.


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## Karter2 (Nov 17, 2011)

efeballi said:


> AFAIK the early Model S'es used Panasonic NCR18650B batteries. ....k


 Tesla, have never used standard panasonic cells, they have always been a custom cell produced by Panasonic.


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## arklan (Dec 10, 2012)

2c discharge is perfectly fine but the 500 cycles is what scares me


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## jhuebner (Apr 30, 2010)

arklan said:


> 2c discharge is perfectly fine but the 500 cycles is what scares me


It's 500 cycles if you use the full 0-100% SoC range (2.5-4.2V). Which no one ever does. Especially limiting the maximum SoC to 90% will triple the cycle count. 

Taken from https://www.dke.de/resource/blob/93...860a39/kompendium-li-ionen-batterien-data.pdf Page 23

Color codes the DoD and label below is the maximum SoC


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## aquabiologist (Sep 8, 2017)

Sooo. Charging to 100% (SOC) and then discharging to 20% (80%DOD) gives 1000 cycles, whereas charging to 80% (SOC) and then discharging to 0% (100% DOD) gives 3000 cycles. Do I read this table right?

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## jhuebner (Apr 30, 2010)

Correct. Staying away from the top end has the biggest impact. It's because high voltage causes stress on the electrolyte.


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## aquabiologist (Sep 8, 2017)

Good to know. Thanks!

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## arklan (Dec 10, 2012)

jhuebner said:


> Correct. Staying away from the top end has the biggest impact. It's because high voltage causes stress on the electrolyte.


does this go for all lithium batteries?


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## jhuebner (Apr 30, 2010)

arklan said:


> does this go for all lithium batteries?


Yes, including LFP.


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## john61ct (Feb 25, 2017)

But LFP starts with a much greater baseline for cycles lifetime. 

Vendors' estimates of 2-4000 cycles turns out to be relevant for very hard usage like EV but in gentle general storage (House bank) use, actual lifespan may be many times that. 

Cool environment, avoiding both top and bottom "shoulders" and low C rates all help.


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