Convince me I need a bigger battery

Based on your usage profile, I'm not sure there's a reason to go bigger. I might suggest a 220 in the garage just so you can charge a bit faster. For example, after a full day's commute, you then need to take a friend to the airport and back or some such. Wiring 220 is awfully cheap to do.

Agree. Assuming you drive <= 75mph (which sounds like a pretty safe assumption)...

WhiteKnight said:

When traveling at 75 mph (highway speeds) you get only 70% of the range you would receive at 55 mph. In addition the battery capacity is reduced by 30% after 6-9 years.

Therefore your highway range (@ 75 mph) with ... the 40 kWh pack you start at 115 on the highway and go to about 80 miles in range by year 8.

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Highway Range Ignorance

Agreed, if you're sure that you aren't going to be taking longish weekend trips, then the 40kWh/160-mile car is definitely the one for you. It's perfect for your needs!

The reason to consider the 230 mile battery based on your daily mileage is the warranty it provides over the 160 mile battery. Using 50 miles a day x 365 = 18,250 x 5 years = 91,250 miles. If you plan on keeping for 7 years that puts you just over 127,750 miles. Well over the 160 mile battery warranty and just over the 230 mile pack warranty. Driving more than the 50 miles a day average would justify in my mind the 230 mile pack over the 160 mile one due to its better warranty.

I agree with ckessel a 220v outlet has the convenience factor to make it worthwhile to install.

Definitely agree on the 240V 50A outlet. Since the charging cable comes with the car, it would be minimal cost to have the outlet installed. I think you'd be fine with the 40 kWh pack but agree that the 60kWh pack might be better for warranty reasons.

The point about the 230 warranty is a good one, but remember that the battery doesn't break down really, you'll just have a little more degradation. Batteries go bad due to a combination of age and use, so you'd just be going over on use. Given you're not deep cycling (full use every day), I'd think even if your battery suffered, it's not going to be dramatic. There's every chance it'll be perfectly fine for your project lifespan (8 years). Plus, you've got the $10k difference in the bag to help if you need to sell a little earlier than expected.

I commute 50 miles roundtrip daily, am home by 7pm each nite, and leave for work at 9am

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Tommy said:

Using 50 miles a day x 365 = 18,250 x 5 years = 91,250 miles. If you plan on keeping for 7 years that puts you just over 127,750 miles.

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work days in a year - Bing

260 working days

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260 x 50 x 8 = 104,000

Just past the 40 kWh warranty, and that's not including the 50-79mi. days and vacation travel.


Very good point, Tommy.

If a 40kWh battery today is $20,000, and cost goes down 8% per year, in 8 years a replacement is likely to be $10800
You can pay $10000 more now for the 60kWh or take your chances that you may need to buy a new 40kWh in 8 years.

I'm not going to try to convince you to getting the large battery.

You don't need it. Especially if you have access to taxis or a rental in case of "emergency trips", which being in Palo Alto, you probably do. You already plan to replace the car fairly quickly, so the idea some of us have (big battery == small battery 10 years from now) doesn't apply. Unless you're in a raging hurry to get your car and are willing to pay $20K for the privilege, the small battery seems right for you, apart from the warranty considerations mentioned by others.

Actually, have you considered getting a Leaf? It sounds like it has enough range for your needs.

I will, however, try to talk you into improving your house wiring. :wink: You want the NEMA 14-50 (220 volt 40 amp actual, 50 amp breaker) wiring if you can -- and it's relatively cheap compared to a car.

The current Tesla range estimates come out at 4 miles per kwH in the battery. If your existing 110s are standard '15 amp circuits', you'll be getting 110 * 12 = 1320 watts of charging, or 1.32 kwH per hour, or 5.28 ideal miles per hour of charging. That means charging for 10 hours every night in order to recover your commute miles, and for 15 hours to recover from a weekend 80 mile trip. This is on the borderline for you, and you'd have to watch your charge carefully. Especially if for some reason you get even slightly worse mileage than expected, for whatever reason.

If you already have the less common 110V *20 amp* circuit in the right place, that would give you about 6.6 ideal miles per hour of charging, which *might* be good enough for you to not bother (12 hours to recover charge from an 80 mile trip). In an older house you might have 10 amp circuits (I grew up with 10 amp fuses), in which case you *must* upgrade (you'd barely be able to recover from your commute overnight).

In contrast, the "50 amp circuit" gives you 220 * 40 = 8800 watts, or 35.2 ideal miles per hour of charging, which would mean you'd never have to worry about it, ever. The car would pretty much always be fully charged even if you had a blackout for two days; and even if you suddenly had to make unexpected trips longer than usual back to back, you could do so without a moment's thought about charge. If you already have a NEMA 14-30 220 volt dryer outlet in the right place, I wouldn't bother doing any electrical work. (21 ideal miles per hour of charging).

If you have to do *any* wiring (for instance, if all you have is a 10 amp circuit), there seems to be little reason to install anything less than a NEMA 14-50, unless you're running up against the limits of your main breaker/fuse.

Edit: of course, you can always defer the electrical work until you see what mileage you're getting! Go ahead and plug into the 110V now, and you can always install the 220V later.

Probably the only argument for the 60kWh pack, in your situation, would be for the resale value. If you're planning on selling the car in 7 or 8 years, the the larger pack with the better performance and supercharger access might still be worth $10,000 or more!

So my first year with the roadster, I went with a simple 110v charger and had no problems charging overnight based on my usual driving profile. On the occasions when I drove a bit more than usual, it was still fine; although I didn't get back to a full charge the next morning, I would always "catch up" on the weekends.

Here is why I bought the 220v/50A charger: (1) I was adding solar power to my house, and adding a 220v outlet to my garage as part of the solar installation basically came for free. (2) Battery degradation is mostly a function calendar-time, number of charge cycles, and time @ charge. With the 220v charger, I now set my car to start charging at 7am (I leave around 8am). Most of the day, my car is sitting with less than a full charge == happier batteries. I am close friends with a number of folks in the battery-tech space who've convinced me that time @ charge is the most important metric for practical battery life extension.

just my 2c -- YMMV.

Another reason to upgrade to 240volt charging is from Tom Saxton's experiments with charging efficiency: Tesla Roadster Charging Rates and Efficiency - Tom Saxton's Blog

Charging at 120volts is just not as efficient. Charging at 240volts 40amps is the sweet spot for charging efficiency in the Roadster. The Model S is likely to be similar, but not guaranteed.

BS Mann said:

I have been reading many different posts and am still undecided about whether to stick with the smallest battery, or even bother with a 220v charger.

I commute 50 miles roundtrip daily, am home by 7pm each nite, and leave for work at 9am, rarely drive more than 80 miles a day, even on weekends. I have no interest in going on long driving trips, getting a supercharger or the air suspension or the Signature red paint. I hope to drive the car daily for 6-8 years and trade in for whatever exciting new car is out there.

It seems like with the smallest battery, a 110 outlet and standard extension cord I could charge it back to full every nite, even after 7 years i should still have enough battery life for my commute, so why would i want to spend extra to install a 220 charger in the garage, or get a bigger battery?

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I think the 40KWh pack is probably fine for you - but not 110V charging. Based on the Leaf - 50 miles per day would take 12-14 hours to recharge. Too close for comfort if you get home late at night. I suppose that if you keep it near full and usually get home at 7:00 it would all even out - but I've found that Leaf drivers who do 25-30 miles per day are happy with 110V - most who do more have 220.

brianman said:

work days in a year - Bing

260 x 50 x 8 = 104,000

Just past the 40 kWh warranty, and that's not including the 50-79mi. days and vacation travel.

Very good point, Tommy.

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260 days a year ? There are 102-104 or so saturdays & sundays, that leaves 261-264 days. Don't you have holidays and vacations in the US ?

230 workdays in a year is the norm over here (Norway), though it obviously varies somewhat from year to year.

If the 160 battery is all you need and would not be taking advantage of fast charging and you do not go over the mileage, and fine with the slower acceleration, it should be fine. The only issue is probably waiting until 2013 for your car.

Personally, the acceleration should be on par with a luxury car in the same price range.

Resale value may be slightly affected, but not significantly. I would expect the 230 battery one, after 8 years to have the range of the 160 and sell for 10 K less than a "new 160" as long as the rest of the car is in great condition.

The 230 battery may not be needed or a waste of money based on your driving habits. (kind of like buying a high end gaming computer and using it as a Facebook/email machine).

Dan5 said:

If the 160 battery is all you need and would not be taking advantage of fast charging and you do not go over the mileage, and fine with the slower acceleration, it should be fine. The only issue is probably waiting until 2013 for your car.

Personally, the acceleration should be on par with a luxury car in the same price range.

Resale value may be slightly affected, but not significantly. I would expect the 230 battery one, after 8 years to have the range of the 160 and sell for 10 K less than a "new 160" as long as the rest of the car is in great condition.

The 230 battery may not be needed or a waste of money based on your driving habits. (kind of like buying a high end gaming computer and using it as a Facebook/email machine).

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the 230 battery is never a waste of money. you will get at least 50% longer lifetime or distance to travel. when the 160 battery pack will have lost 30% = 90miles, the 230 pack will have lost only 20% or less = 180-190 miles, still more then the 160 when new.

I don't need a bigger battery for my commute either (even the 100mi Leaf would have been fine).

I don't really know what circumstances the Model S's mileage is quoted in (some standardized driving profile, I'm sure, with the usual "your mileage may vary"). Having the extra power in the battery, even with a short commute, means you never have to think about:

- Using the air conditioning or heating whenever I want, even on longer-than-normal trips
- Forgetting to charge once in a while
- Driving inefficiently (faster starts, windows/sunroof open, etc)
- Driving in non-ideal conditions (cold/wet, hilly terrain)
- Driving with 5 people on board.
- Reduced "anxiety."


... in other words, a bigger pack can help you think less about current "limitations" of EVs. When coming to my decision, I de-rated each pack's mileage in my head by 1/3. The middle-size pack was my original choice even though I could handle most of my driving on the small pack. I think it had the best value-for-money of the three.

/Mitch.

The pure joy of driving electric (to me) means that I will drive more...even casual "drives just for the sake of going for a drive" (a la Roadster).

A bigger battery = more freedom...to drive more when I want to drive more (and have more guilt free fun).

A bigger battery means the car has has fewer operational (range) limits..I don't like limits...they're so limiting! :wink::biggrin:

Therefore, give me the biggest battery & the fastest recharge capability...:smile::smile::smile: