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By Russ Finley on Feb 26, 2012 with 13 responses

How to Turn a Tesla Battery Pack Into a $40,000 Brick

Li-ion, Not Your Father’s Battery

This Tesla-to-brick story first appeared in the Understatement blog, authored by Michael Degusta. Some rich guy, too busy to read his owner’s manual, parked his six-figure sports car in a garage for six weeks while his home was being remodeled.

From the Tesla owner’s manual:

“Keep in mind that when the vehicle is left unplugged with a full Battery, the initial rate of decline can be significant. When fully charged, the Battery’s charge level can drop as much as 7% a day and 50% within the first week. When the Battery’s charge level falls below 50%, the rate of decline slows down to approximately 5% per week. Over-discharge can permanently damage the Battery.”

That equates to a ruined battery in roughly 11 weeks. In other words, for this Tesla to be damaged in six weeks, it was likely parked with a mostly discharged battery. Ouch.

So, what does that picture of my electric bike have to do with all of this? It’s powered by lithium  ion batteries. You can’t let this kind of battery drop below a certain voltage or it will be ruined. I’ve been using these batteries for five years now and they are going strong.

Specifically, my pack consists of six Dewalt 36 Volt lithium ion power tool packs. Each pack contains ten cells connected in series. I connect pairs of packs in series and then each pair connected in parallel with the other pairs. Each tool battery comes with a built in circuit board called the BMS (battery management system). In fact, all lithium ion battery packs come with a BMS designed specifically for that pack.

Some BM systems continuously use power and if you leave the pack on a shelf too long it will drain the voltage down low enough to permanently damage the cells. The Dewalt BMS when being used on a Dewalt power tool will turn off the pack before it can be damaged but a tiny current may still be flowing in the BMS circuit board.

The Tesla uses 6,831 itty-bitty cylindrical cells compared to the Leaf’s 192 much larger prismatic cells. No two cells (batteries) are identical. Weaker cells in series with other cells tend to get hotter than their neighbor’s and begin to degrade faster, creating a feedback loop and a rapid downward spiral to failure. One bad cell in series with other cells will cause them all to fail in short order. The more cells you have in series, the worse this problem gets.

To prevent the weaker cells from causing a failure, the BMS continuously measures each cell and sends a little charge to any that are dropping lower than their neighbors. My guess is that with 6,831 cells, the Tesla BMS stays very busy, and uses a lot of energy. On the other hand, the Leaf owner’s manual also warns not to “leave your vehicle for over 14 days where the Li-ion battery available charge gauge reaches a zero or near zero (state of charge).”

To be perfectly honest, Tesla should have done (and probably will do in the future) a lot more to warn owners of this potential.

  1. By rmaytard on February 26, 2012 at 3:37 pm

    I wouldn’t want one if I lived in a snow belt.  Here in the northeast it’s not uncommon to have a week + long power outage every few years from bad snow and ice storms.  They need fix the design problem like other car manufacturers have.  
    New battery = $40KBad publicity = priceless 

  2. By Eric on February 26, 2012 at 8:48 pm

    The future is here and its not perfect – imagine that! I put my down payment on a new Tesla Model S and I can’t wait for this to be my main source of transportation. I live in Santa Cruz, Ca. and know with a 230 mile range per full charge, I will get anywhere I need in the Bay Area. 
    As for the big worries of the battery bricking problem – I will be quite aware of how to keep my car charged and won’t be in a position of not using it for more than 11 weeks. With new technologies come new responsibility. This is the most excited I’ve about a car in my life time and its created and made here in Fremont, Ca. Doesn’t get more patriotic than that. Manufacturing is alive in the US and the future is green energy with amazing design. I have no doubt, this is a car worth its risks…… 

    • By Not Eric on February 27, 2012 at 12:05 pm

      Hay Eric,
      That car is mostly made in England and imports parts from other places. It’s as American as my Honda built in Tennessee and more American than my Mom’s Mexican ford. 

      • By Me on September 10, 2012 at 6:01 pm

        The Model S is entirely made in the USA. Visited the plant myself. Get your facts straight buddy.

    • By Russ Finley on February 27, 2012 at 9:02 pm

      You got to empathize with the guy. Typical of males of my species, I usually don’t read instruction manuals either, preferring to iterate to a solution : )

  3. By david slagle on February 27, 2012 at 8:37 am

    I have several gasoline operated cars that are now bricks.The cost to refuel
    these vehicles is uncontrollable and has become unaffordable The cost for gas is
    the reason a person needs to search for a alternate source for propelling their
    transportation. Charging a Tesla off solar panels purchased with a federal solar
    panel rebate is another good reason to go electric. While your not charging the
    Tesla use the energy from your solar panels to power your home. Tesla never said
    it was cheaper to operate over the long haul but it does allow for your control
    of refueling expenses. You also gain an asset in solar panels rather than
    watch the smoke from your oil burner fly away. You’ll soon get the picture or
    the middle east will own you. Stop this oil madness!!

  4. By william rovin on February 27, 2012 at 10:58 am

    I’ve had my Tesla Roadster for almost 2 years, and it is my daily driver.  My electricity costs me approximatelly 2 cents per mile.  This is the most awesome car ever made, and the only person who would let their batteries go dead are not drivers, but collectors, who don’t read their manuals.  In storage mode, you plug the car in, and it keeps the batteries at an optimum level.  Trust me, nobody who has ever driven a Tesla would ever say anything negative about it.

  5. By mac on February 27, 2012 at 2:13 pm


    Battery breakthrough ?

    Envia Systems claims they have perfected a 400 Kw/hr lithium battery that promises to cut in half present Li cell costs and increase range of EVs to 300 miles.

    If this is for real, it’s is a significant breakthrough.

    Here is are some links:

    Envia Claims ‘Breakthrough’ in Lithium-Ion Battery Cost and Energy Density

    Battery breakthrough could bring electric cars to all

    Startup Envia battery promises to slash EV costs
    Read more:

    • By Russ Finley on February 27, 2012 at 9:46 pm

      That’s an interesting link. Hopefully, these first Leafs and Teslas will be viewed with mild amusement someday. Maybe there will be battery upgrades available when the time comes. I paid $400 for a digital camera 8 years ago that took ten low resolution pictures and chewed through four AA batteries  to do it.

      Press releases are a dime a dozen and meant to raise funds. Don’t get excited until you can actually buy the product.  I followed the development of the A123 battery for years and then one day, there they were. I bought them at a tool store and have been blasting around town with them for many years now.

  6. By Michael on February 27, 2012 at 2:57 pm

    Doesn’t the Tesla Roadster have a power generator to prevent this kind of thing from happening?

  7. By MC on February 27, 2012 at 5:03 pm

    Tesla responded to the bricked battery in a blog.   Bricking a Model S (or Model X) should be very difficult.  From the blog:
    ” … a Model S battery parked with 50 percent charge would approach full discharge only after about 12 months. Model S batteries also have the ability to protect themselves as they approach very low charge levels by going into a “deep sleep” mode that lowers the loss even further. A Model S will not allow its battery to fall below about 5 percent charge. At that point the car can still sit for many months. Of course you can drive a Model S to 0 percent charge, but even in that circumstance, if you plug it in within 30 days, the battery will recover normally.”

  8. By mac on February 27, 2012 at 5:53 pm

    “perfected a 400 Kw/hr lithium battery”

    Should read:  “perfected a 400 watt-hours per kilogram (Wh/kg) battery”

  9. By mac on February 28, 2012 at 7:39 am

    Russ said in reference to the Envia 400 Wh/kh battery:

    “Press releases are a dime a dozen and meant to raise funds. Don’t get excited until you can actually buy the product.”


    That’s pretty sound advice.  You may have heard this old battery joke  It goes something like this:

    They held a liars contest one year and the two finalists were a used car salesman and a battery salesman,  Of course, the battery salesman won hands down.


    Battery start-up claims should be taken with a grain of salt.  On the other hand, when well established battery manufacturers like LG Chem, Sanyo, Saft or Toshiba make an announcement, you can usually take it to the bank. Several months ago, Toshiba announce they were coming out in 2013 with a new Li cell that can be re-charged in just 15 minutes.  I believe them.

    As far as digital cameras eating up AA cells goes, what I finally did was to buy some Sanyo 1100 ma Nimh rechargeable cells good for 100 charge/discharge cycles and a Maha charger.  The rechargeable cells (pkg of 4) only cost me about ten bucks,  The charger was $30 but it pays off if you take a lot of indoor flash pictures, 

    Both the cells and charger are now out-dated.  There are now  Ni cells well over 2000 ma rating and the new smart chargers will read individual cells.  My charger will only charge in pairs (2 or 4 cells) and when any given cell is fully charged it shuts off leaving some cells potentially undercharged. If I had it to do over, I would buy a new smart charger and larger capacity cells.

    I use the rechargeable cells for everything … flashlights, electric clocks and so on.  I just got tired of running to the store.

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