Battery Charge/Discharge Cycles

Battery Charge/Discharge Cycles

A refinement to the batter life question question is, after how many charge/discharge cycles does the charge capacity reach 20% of its original capacity?

We can then divide that number by our respective number of charges per week and arrive at a life duration.

If you could provide a graph with capacity over charges, that would be great, since others may wish to use a different % as the minimum. For example, someone with he 160 mile battery might want a minimum 45 mile range, and thus 30% is their threshold for wanting to buy a new battery.

A decay graph would also help us choose which battery to buy based on cost-justification and computing the expected life.

Straight Shooter | July 28, 2010

I'd also like to see if DOD effects the life of batteries. If we never let our batteries get below 50%, will they last forever? How many 95% DOD cycles will they take, as most folks going to trips will plan their stops based on the onboard computers estimate of the remaining range. This is no different then letting your gas guage get to almost E before to pull over at a gas station. You know people will do the same thing.

Brian H | August 4, 2010

Actually, the batteries are considered "expired" when they reach 70%, a 30% drop. You could trade them in to be recycled, or use them as power storage for your home PV setup!

jkirkebo | August 5, 2010

My thinking is like this: When the car is new, there is no (or very few) fast chargers around and I need the 300 mile range. After maybe 7 years, the pack is a 70% and provides 210 mile range. But many fast chargers have appeared and 210 mile range is more than enough. Some years later (10 years from new?) the pack is a 50% and I thus have a 150 mile range. Even more fast chargers have appeared and the range is still good enough.

The 300-mile pack has to degrade down to 33% to give identical range to a new Nissan Leaf TODAY. Still it would probably be useful to many. I wonder how many years it would take for the pack to degrade that far ?

Todd Burch | August 8, 2010

With current battery chemistries, a lot of rapid charging will degrade the batteries faster--particularly older batteries. Lithium-Ion battery technology hasn't quite progressed enough to allow for that many rapid charges.

I think what's more likely is that by the time your battery reaches the end of its useful life, battery technology will have progressed so that it will allow for more energy storage at a cheaper price. They most likely won't be lithium ion batteries.

In 7-10 years, you might be able to purchase a battery with a range of 1,000 miles and that can be recharged many more times...all at the same or lesser cost than the upcoming 300 mile pack.

Think of it this way: You're buying the equivalent of a "car phone" (remember those?). By the time your battery's ready to be replaced, the battery equivalent of smartphones will be on the market.

It's another reason electric cars are such a good idea: You can essentially upgrade to larger and larger gas tanks in the future without buying a new car.

jkirkebo | August 9, 2010

The 300-mile pack is supposed to fast charge to 80% in 45 minutes, that is about 1C of charging when you take out the unused part of the batteries. Is 1C really that fast ? My laptop and phone charges in about an hour...

Still, at 200 mile range, I would need to fast charge about 15-20 times a year, at 100 mile range maybe 50 times a year. Not that big a deal I think.

fnfargento | August 10, 2010


Timo | August 10, 2010

One important thing in full DOD charging is that with bigger battery packs you do that a lot less than with smaller packs like GM Volt pack. Assume 300 miles with single charge. 100000 miles would then be just 333 full DOD charges. Same with Volt 40 mile battery is 2500 charges.

If you get 600 mile battery you halve that figure for same mileage improving battery pack performance and durability. Bigger is better :)

Timo | August 15, 2010

@fnfargento, please do not yell, and please learn how to write properly. I have no idea what you mean by "AND THEN U CAN PUT A FLEXIBLE THIN SOLAR PANELS EN THE EXTERIOR OF THE CAR, AND IN THE INCLINATION ROAD" other than you mention solar panels. Inclination road?

There is no such thing as free energy. Guess what "regenerative braking" is? It is motor used as generator. Driving with brakes on is generally considered quite stupid.

Solar energy is weak. You might get enough energy from solar panels in car surface to light car headlights (in a good day), but not much more. And they cost a lot. If you want to get practical amount of energy you need a lot bigger surface area. Maybe in future as car cover "blanket" or something like that (and it needs to be cheap enough that nobody steals it).

Dark_Elf | August 18, 2010

Solar energy is weak ?

Agreed it would take a bigger array to make it really give enough energy to really do a difference, but there is a lot of people around the globe working on some way to make it better all the time.

The biggest problem is actually more the solar Panels its self. Solar Panels doesn't give directly any energy, they produce potential differentials witch gets converted to a current. If the car gets solar panels on it, in order to get high enough currents it really has to get lethally high voltages around it... making it a really hard engineering job to make it safe as well.

just a little input.


Timo | August 18, 2010

@Dark_Elf; solar power is weak. Only about 1000W/m^2. 1kW. At max in good day and in directly facing sun in desert. In normal car you could get maybe about 400W/m^2 from any reasonable surface at midday in mid US at summer in sunny day and after that you get the conversion losses, so by covering entire topside of the car with solar panels you might get something like 800W at midday in sun. Put that car in shade and you get a lot less. Get it dirty and you get less. Drive at night and you get nothing.

That's about 20-30kG worth of battery for entire day production and costs a lot more. And probably weights quite a bit more too because of needed supporting and protecting structures.

Entirely different thing is to put panels to place where you can direct them to sun and surface area is not an issue. There solar is basically free energy minus manufacturing and maintaining expenses (energy and money).

Brian H | August 20, 2010

MIT, Stanford, and others have come up with major improvements in LiIon battery design. I'm confident that by the time your 5-yr. minimum battery life expectancy is up, there will be packs available with 3-10X the capacity. Note that the limitation on charging times is the connection and the battery design itself. It takes BIG amperage and voltage to pump 50 or 100kwh into a battery in a few minutes.

It's just arithmetic; if 240V at 35A takes 5 hours to charge your car, and you want to do it in 15 minutes, you have to increase the other numbers by a combined factor of 20 somewhere.

Unnefer | August 29, 2010

Now to complete the design, I believe Lightweight solar flexable/foldable panels for the roof will do the magic.

Unnefer | August 29, 2010

I believe you will generate more power with lightweight solar panels structured AS the roof then you would without. This much asked for and needed energy that can be used to power the leds/radio, anything is better than nothing.

Please do not take offense, we hopefully are all here to make the best out of a good thing.

Timo | August 30, 2010

@Unnefer, main problem with solar panels is not that they do not produce electricity, it is the cost of them.

For that same price you can get a lot of batteries. I once saw a document which says that cheapest current solar panels are about $2/watt. That means (for entire roof, before losses of being a car roof) about 675W (30% conversion which is high) * 2 = $1350. Energy you would get maybe about 800Wh in good (24h) day. That same amount put into batteries would be something like (based on numbers from Wiki) around 2kWh, probably more. Over twice the same amount. And you wouldn't need to park in the sun for it.

It just isn't worth the money (or added complexity or cost of building or difficulty of replacement or keeping it clean).

If they get the price down and conversion ratios up, then maybe. OTOH also battery prices / Wh will go down, so you have same thing for future also.

cmotown1 | October 18, 2010

Why not use a set of dual batteries with a switchable alternator to help with charging??

Timo | October 18, 2010

@cmotown1; Didn't quite understand your question. Dual batteries? Switchable alternator?

Vawlkus | October 19, 2010

More batteries = more weight = less range & speed.

The engineers have already determined the optimal weight for a battery given their motor & the weight of the car, so you're not going to increase that without new technology in the battery (which is being researched like crazy).

Brian H | October 19, 2010

cmotown thinks he/you/anyone can charge one set of batteries by running the alternator while driving on the other set of batteries. Just more free energy nonsense.

Brian H | October 19, 2010

testing formatting HTML.

Brian H | October 19, 2010

OK, Timo, basic HTML works. <br> does a linefeed, and <p> does a 'Return' break.So paragraphingIS possible. :)

Brian H | October 19, 2010

Testing That's <b> for bold, and this is <i> for italics.

Timo | October 19, 2010

Good to know that HTML works. Thanks Brian.

bcn0209 | October 30, 2010

jkirkebo says he thinks he will have this car 7 years? After 7 years you will have had like 2-3 battery packs! So include that cost in your initial purchase. It amazes me to have people think the battery will last that long. I would think that Tesla would have to have a pack that starts out around 400 miles range and degrades to 300 mile range over its life during day use and 350 mile range at night dropping to 250 over the packs life.

Li-Po batteries do degrade, even with proper care.

bcn0209 | October 30, 2010

Lets say a new battery costs you 5,000. If you need one after say...3 years, that's about 36,000 miles of normal driving. 5000/36000 = 13.8 cents a mile...that to me seems radically low even when adding the price per KW hour to drive. Your looking at a cost per mile (vs. gasoline) of less than 10% of what a gas car would cost in fuel. Now, knowing that a 300 mile range batter pack is going to require something on the order of a 2000amp hour battery...HUGE...and the cost of Li-Po batery cells, I bet the pack is going to be more like $8-10K! Even then, 36,000 miles/10,0000 bucks is only .36 cents per mile.

Sounds encouraging

Roblab | October 30, 2010

LiPO batteries? Hmmmm. I heard Li/poly. And why does it only last 3 years? There are many RAV4EVs on the road with 100K, 150K miles after 8-10 years, of course NiMH batteries, but who's to say? And who says the battery will cost $5K to replace? Tesla is guessing $7K or more. Lots of conjecture and imagination. Wait a bit. You will know a lot more as Tesla gets closer to production and you won't have spent a dime, so you can always back out.

Timo | October 30, 2010

@bcn0209; Roadster battery lasts around 50000 miles over 70% capacity. It depends how you drive your car how many years that takes, but I don't think many people drive over 25000 miles / year as you seem to assume. 300 miles require around 75-85kWh battery. It's big, but not huge. Physical size of that isn't really very large. For Model S we really don't know yet which kind of battery chemistry will be used and how long that lasts. All I know about those batteries is that they are heavily modified cells (from Elon Musk interview where he said things about Model X). Li-ion, not LiPO.

Dan5 | November 1, 2010

Do your homework- they ARE NOT using Li-Po batteries for the Model S.
Google Panasonic and Tesla.
Here's the link

For the Roadster the batteries of lithium cobalt oxide and for the Model S, they are lithium nickel which can with stand about 500 charge cycles before a noticeable degradation (at that point you are around 70% charge)
500*300 miles/charge= 150,000 miles

150,000 miles is very reasonable for a car- that's better than the US government average for a car! Heck, I knew someone whose ICE engine blew at 70,000 miles, and from my own experience my old car started failing big time at 100,000 miles. Given I would prefer if they used Samsung's Lithium Titante, (despite the fact I dislike Samsung and love Panasonic) but those are too costly presently.

Vulpine | June 23, 2013

Some of you have very interesting and logical arguments; some don't.

BCN's arguments simply do not fit any established EV experiences as batteries such as used in the Toyota Prius (and licensed brands) have already demonstrated 7-year and longer lifespans in everyday use. Now, I'll grant that rapid-charging them in the manner of Tesla's Supercharging stations will be hard on those batteries in the long term, but then the average driver simply isn't going to be doing it that way when they can charge overnight at their homes or during a normal office workday if their employer's parking area includes a compatible charging station. Odds are than any one owner might only use a Supercharger Station only a few times in the lifetime of the vehicle--especially if it is used as a commuter car where a 200-mile range more than meets the need for two days or more of conventional commuting or typical homemaker shopping. In my own case, a 200-mile range almost easily covers a full week of my typical driving, though taking a weekend trip to my in-Laws would strain the full range of the battery on a round trip but could still let me restore some mileage by plugging into their home's standard power outlet. (Admittedly, at 5 miles per hour of charge, it would take almost 30 hours to handle the one-way return trip.) Considering that currently the nearest Supercharging Station is only about 7 miles from my home, the need to use it would be minimal but the location convenient if I did have need.

However, it's more the numbers of his arguments that fall grossly short of the reality. The battery pack by itself is likely far more expensive than a mere $5000. I'd expect it to be closer to $10K due to the much longer available range than a Volt's or Prius' battery and possibly even more. If the typical user only drives 1,000 miles per month (still the national average) then that means only 3.3 charge cycles per month if you drain it to the near-empty level which is the recommended usage of most rechargeable batteries. Even if you do a full charge just once a week through the standard charging system you're only pulling the battery down to about the 20% level which is considered nearly ideal for giving your battery the longest usable life. This also means that the battery pack should again last far longer than a mere 2-3 years which is what BCN offers.

Brian H | June 23, 2013

Vulpine & Dan5;
OK, but a few quibbles:
The chemistry is modified, not the same as any of the standards you refer to. Elon cited a test vehicle with 500,000 miles without excess degradation, e.g., n.b.

And full discharge is far more harmful than full charging; 20% is safe.

There is no experience, so far, of ANY harmful usage pattern, in fact. We await (for several years to come) any such reports with bated breath.

Vulpine | June 24, 2013

@Brian H: It's not that hard to program a computer to essentially shut down when the battery reaches about 5% of full discharge. Since the Tesla automobile is essentially a computer on wheels, the technology should be simple. Sure, 20% is safe, but wastes what could be the equivalent of a small backup reservoir similar to the arrangement most motorcycles have where accessing a point lower in the tank gives you about a half-gallon or about 20 miles of additional range to reach a gas station.

The point is that the battery swap technology in a Supercharger Station could ensure the battery gets the longest possible usable life by essentially eliminating the conditions that create a battery "memory".