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Ok, so think of this scenario:

Bob and John are neighbors. They get a Model S 300 mile pack, sports version, at the same time. They both drive to and from work 5 days a week, 45 weeks a year. Bob is a hothead – he loves to floor it, he drives fast often going >130 km/h. John is careful and calm, drives “eco-friendly”, rarely goes fast, uses a lot of regenerative braking.

Bob has only 25 km a day to drive, while John drives 50 km per day. However, due to their different driving styles John manages to do this using the same amount of energy as Bob (i.e. twice as efficiently) so that when they come home every day both cars show 50% capacity. They both charge over-night and both start each day with a standard charge of some 80%.

Now, after say 3 years, who’s battery will be in the best condition (that is the least “worn”, best residual capacity, best performance)?

Mind you both neighbors have had the exact same total energy consumption during these 3 years – the exact same amount of charge-discharge to the battery.

Is it:

A) John’s – because he has driven more carefully and put less “strain” on the battery.

Both packs will have the exact same condition because they have had the exact same amount of charge-discharge.

C) Bob’s – because he has driven half the amount of km and done this in probably less than half of the time.

This is not a trick question by the way, and I don’t know the answer (that’s why I’m asking).

Bob and John are neighbors. They get a Model S 300 mile pack, sports version, at the same time. They both drive to and from work 5 days a week, 45 weeks a year. Bob is a hothead – he loves to floor it, he drives fast often going >130 km/h. John is careful and calm, drives “eco-friendly”, rarely goes fast, uses a lot of regenerative braking.

Bob has only 25 km a day to drive, while John drives 50 km per day. However, due to their different driving styles John manages to do this using the same amount of energy as Bob (i.e. twice as efficiently) so that when they come home every day both cars show 50% capacity. They both charge over-night and both start each day with a standard charge of some 80%.

Now, after say 3 years, who’s battery will be in the best condition (that is the least “worn”, best residual capacity, best performance)?

Mind you both neighbors have had the exact same total energy consumption during these 3 years – the exact same amount of charge-discharge to the battery.

Is it:

A) John’s – because he has driven more carefully and put less “strain” on the battery.

Both packs will have the exact same condition because they have had the exact same amount of charge-discharge.

C) Bob’s – because he has driven half the amount of km and done this in probably less than half of the time.

This is not a trick question by the way, and I don’t know the answer (that’s why I’m asking).

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## Comments

If you go uphil on your way to work, you are probably going downhill when you're going home, right? If it's steep you might be able to recover some range there with battery regeneration though.

I think, always keep the car as full as possible and put the pedal to the metal!

OP post, I would say that A) is right answer. Less strain in battery wears it down slower. Difference isn't large if both use same battery settings though (no performance mode for Bob). Bob would destroy his brakes and tires though, while John brakes and tires would be in much better condition.

Driving it harder requires both a higher C rate (discharge rate) from the battery, and also heats the battery up more due to internal battery resistance. Both of these effects are harmful to battery health.

However, the DEGREE to which it is harmful is an open question. it may not make a huge difference...or it might.

Depends on a lot of factors, including Tesla's battery cooling capability, and the C rate when flooring it compared to the max C rate capable by the battery.

Either way, A is the right answer.

If you look at it from force-POV you apply extra force going uphill and equal amount less force going downhill because for both situations gravity is the force you are dealing with and it doesn't change between two cases and force-vector stays same.

All that does matter is does that force exceed losses going downhill, in which case you need to start accelerating uphill in order to prevent car from accelerating. If this is the case you have to apply extra force in same direction going up and going down, and that is a losing game because regen is not as efficient as accelerating (otherwise it wouldn't matter).

Also there is factor of engine efficiency and power applied. In this case you could actually "gain more" going down than going up. Never more than losses (2nd law of thermodynamics), but saying it other way you might "lose less" going down relative to going up. That could give you actually <b>better</b> result from hills than from flat, but that is not very likely in reality.

Sorry I know it's vague since I can't tell you the exact detail of every road I drive, but I guess I am just wondering how significant the impact is. As you mentioned, driving downhill could provide regen energy, and the electric motor in the Tesla is way, way more efficient than any ICE in other cars.

I'm not even expecting that someone know the answer I'm just wondering aloud. Putting it another way, say that in Nebraska, a someone gets 300 miles with his Model S. What can I expect to get? 280? 200? 100? Obviously it depends on many factors. Like I said, I guess I'm just wondering aloud.

To make that even better is that you gain some of it back going back down.

In fact if climbing hill requires less speed (by speed limit), lets say 55mph instead of 75mph flat you might actually benefit from it because then in flat you would have bigger losses.

Formula to calculate potential energy is U = mgh which gives you energy in joules. One kWh is 3600000 joules.

m = mass of object in kilograms

g = acceleration of gravity in m/s^2

h = height difference of the climb in meters

Lets say that Model S weights that assumed 4000 lbs and you climb one kilometer high hill.

That's then 1814kg*9.81m/s^2*1000m = 17795340 kgm^2/s^2 which is joules. 17795340 / 3600000 = ~4.9kWh.

If we assume you get 60% back going downhill that's 1.9 kWh extra lost caused by that hill during your round trip to that hill.

If then we assume again that hill was 10 degree angle average you travel about 5.8 km for each climb, so twice that is 11.6 km.

...this starts to sound worse than I expected. 300Wh/ mile in flat = 480Wh/km + 2000Wh/11.6km = 407 Wh/mile. If 300Wh/mile gives you 300 mile range that's 90kWh. 90kWh/0.407kWh/mile = 221 mile range.

That should not be too far from reality.

Friends with a Prius tell me they get the best mileage using an accelerate/coast/accelerate/coast cycle. If that's true, then one may get better range in gentle hills. (This doesn't accord with my intuition, but ....)

90% engine + 95% PEM + 95% battery would indicate higher result though. Around 80%.

Does anybody actually know the real regen efficiency? I just have vague memory that it isn't as efficient as normal acceleration.

When you have to drive relatively slowly on winding and narrow mountain roads, consumption is lowered by reduced drag.

Driving prudently in range mode I ended up in one longer drive across three passes with about 160 Wh/km (260 Wh/m). On another shorter run in standard mode I logged about 180 Wh/km (290 Wh/m). Of course always measured once down in the valley again.

The effect resembles a bit the "ice and snow effect". On icy roads you have to slow down and that tends to offset some or even all of what you might spend on heating and defrosting.

- Alfred

http://web.me.com/alfredar/Alfreds_Pages/Blog/Entries/2010/7/4_Tesla_Roadster_Alpine_Road_Trip.html

If I assume that Tesla will size the A/C such that "Standard Mode" sporty driving will not push battery temperature into an "accelerated aging" zone, I would consequently also not expect any easily noticeable effect. Battery life would remain roughly proportional to charge throughput and calendar life.

- Alfred

If that's the case, and if a driver were to drive either the Sport or Regular the same way (hah!), would the Sport's coolant capability make for a longer lasting battery? I doubt it's much of a difference, though.

The 65% is what is recall also. But I suspect that the more gentle the regen, the more efficient it becomes. E.g., lower regen rate over a longer distance should not require as much battery cooling, etc.

I'm quite curious. I understand normal "full" charge isn't really max capacity, but under certain circumstances....

I think I read something along the lines that when you live uphill, you can configure the car to charge less such that you can fully exploit the energy that comes "for free" when driving downhill, and end up with a full battery at the bottom.

("For free" is in quotes b/c it isn't really for free, obviously. You have to use energy to get uphill in the first place. But at least you can recover some of that when going down again, and that will reduce your electricity bill.)