Join The Community

Battery Life Driver - Age or Mileage (Charges)

What do people think will be the driver for the life of the battery, its age or its mileage (or rather number of charges)?

I put pretty low miles on my car, about 6,000/yr., so that the battery lasts a long time is more important to me than that it lasts long miles/charges.

Put another way, 10 years into my 5-series BMW, I have driven 60,000 miles. In combined driving it averages a bit above 20 mpg, but lets use 20 and estimate I've bought 3,000 gallons of gas in that time. Let's say the average price over that time is $3/gallon (I think it's actually a bit less). So I've spent $9,000 on fuel. I haven't, nor do I expect to, replace the gas tank (storage compartment for energy) or engine (user of energy) anytime soon.

Now lets say I'll pay 10 cents per KWhr over the next 10 years, so it will cost me about $7/to fill up the 85 KW battery pack (the useable middle 80% of charge) and lets say I get 250 miles out of that. So electricity will cost $1,680 to drive 60,000 miles the next 10 years.

That looks like I'll save over $7,000 on fuel costs, and perhaps it will be more if gas keeps going up, but this is where my question comes in. Will my 85 KW battery back be at about half its expected lifetime (60,000 miles of 125,000+ estimated) or will it be over the hill (10 years old vs. 8 years promised)? Because even if replacement 300 mile packs are only $10,000, 10 years from now, the cost of fuel (electricity) + storage device (battery) will likely do no better than wash the ICE cost of fuel (gas) and storage device (gas tank). In this exercise, I have chosen to ignore the cost of other repair issues in the costs of ICE vs. EV.

So where this is leaving me is: Since I don't drive a lot of miles, I can't buy this car because it will save me money - I have to buy it because I love it.

Well, I'm OK with that.


Thank you Brian H. Much, much better.

The EV World article rates a C-, at best. Anyhow, the analysis on Teslarumors is much more relevant and thorough. Without all the tendentious opinionizing.

I'm a sponge just gathering and absorbing information. :) I have also seen the tesla rumors info, it is very compelling.

5840 charge/discharge is the conceivable max I believe for anyone (8 years * Twice a day * 365 days). Does not include small regen charging I believe TM has a patent/patents in this area to counteract the affect on any given segment/cell.

Then, some % of that will be for range/performance (HPC/Super Charger) which *most likely* would cause more of a deep cycle to the Li-Ion cells. Like driving until nearly depleted and then pulling up to a HPC/SC and leaving with a full pack 10/month or 100/year or 1000/8years. Say 10% HPC/SC usage for range/performance where a majority of the packs sections (assuming 11 segments from their patent info) and deep cycling degrading the segments cells faster (at what rate I don't know but would assume it's not that much greater since Li-Ion resists and can be buffered by more cells which I believe TM has done; maybe 10% say)

Then assume the little old lady from Pasadena scenario where Model S has been sitting for 8 years, has been plugged in consistently at 110 and has 10K miles.

Take both packs and measure their effective range and estimate their usable life.

This is what I believe TM most likely did when coming up with their warranties. So, I'm not worried while in warranty, but would generally reduce my use of the range/perf charging scenarios when out of warranty.

Finger in the wind guess is that if you get the 85kWh pack and push it to 150K there will be issues (decreased range/power) or 60kWh pack nearing 125K in 6 years. Both scenarios imply high HPC/SC use of at least 50/year or more.

Thanks for the post VB, so based on what you posted: How would you calculate which battery pack to purchase? (BYT)

My rationale for deciding on the battery pack is actually independent from my current driving needs. I apply the same rationale whether I buy an SLR camera, a memory card, a CPU, or a hard drive... Always purchase the largest/biggest/fastest option you can just barely afford at the time of purchase. Then keep it for a looong time. If you think it's not worth the money, then you don't actually need it: Choose a different item instead (compact camera instead of SLR, VW TDI instead of Model S).

The key is to keep cool when technology is evolving (and is getting cheaper): You must find comfort in the fact that whatever you bought, it was the best item your money could buy at the time, and just because technology moves on it doesn't mean that your particular item loses any value for you. It's important to distinguish practical value from resale value/replacement cost.

With this strategy, I have never felt buyer's remorse and I tend to keep my purchases long enough to easily justify the high initial price, and even see some savings over a cheaper choice that would have needed replacement much sooner.

You are very wise Volker.Berlin, thanks for the reply. Leaves me with more questions about my decision however as I am not sure yet how to go. Battery pack that I can get by with, or go performance because that is important to me. I guess the real question is this: Is it worth a little over $10k more to me? I think I have decided that I can barely get by with the 160 pack but would be comfortable with the 230 pack but I'm a speed and performance junkie so I REALLY want the performance pack... :) That and I like the 21" and the black leather with red piping and would have opted for a few other options anyway that are standard in the performance model. I most likely will end up talking myself into being practical and get the base 230 pack Model S with some options that I feel I need.

@BYT There are only things to consider regarding the performance upgrade, assuming you have the $10,000 to spend:

1) you only live once, so use Volker's advice and get it if you can afford it.

2) what would you spend the $10,000 on if you didn't use it for the performance version.

For me:
1) I should get the performance package.
2) Says my kids need to go to college, & I want more cool blinky lights for my Xmas display.

I can put off more blinky lights until next year, but the kids college is harder. I can put the money into their account now and let it grow, or I can put it in later and it won;t grow as much.

@BYT --
When I first saw the S info and found that there was still room on the Sig list, I went for it. Didn't get the options/pricing shock until 3 months later. Sig holders are paying a premium to get the cars earlier, which I've come to accept as an early adopter premium. At the same time, however, it appears the performance S is actually a pretty good deal -- get lots of nice upgrades for relatively less money than those Sig guys like me are paying.

But if the 230 battery pack is a stretch then the extra $15K is going to be a relatively large stretch that could hurt. For 15K could get all sorts of other options on top of that 230 battery (pano roof, home charger, tech pkg) plus have cash left over. And so what about 25% more acceleration! (5.9 vs 4.4) ;-)

Yeah, it's that 4.4 number that has me salivating! I also would be the type to test that 4.4 on a regular bases, this is why my wife hates the fact that I am currently driving her car and can't wait for me to get my Model S and leave her poor baby alone.

I should also build into my budget for those tires since, again, I would be testing that 4.4 second time on a regular basis... ;)

Just had a bit of rain here in California so I got to "test" the traction control on the VW TDI (already did that one, Volker.Berlin!) a few times.

I really like traction control. I'm going to "test" that a bunch on the Sig Perf, I think. To accelerate ridiculously fast in the rain is fun for me now, and will be fun with the Perf.

GreenCarReports: "How Long Will Your Electric Car Battery Last? Science Is On The Case"

I'm still convinced that "it depends" is the right answer to the original question, but if you drive 200k kilometers (125k miles) in only four yours, mileage (No of charges) is bound to become the dominating factor!

This German guy did it with his Roadster, and he claims that his battery pack is left with about 70% of its original capacity:
(German only, not sure if there is a similar article in English somewhere.)

"in only four yours" is supposed to be "in only four years" I suppose.

Timo, absolutely. Thanks.

X Deutschland Site Besuchen