Battery Question

[pkalhan]

Hello All,

Quick question on the battery. I have heard and read that when charging your Tesla, it is best to charge to about 80% (or anything other than 100%) to preserve your battery. My question is, what if you were to get the base battery for the Model 3 (say 40kWh) which gets you the "at least" 215 miles, but this battery can be upgraded (or unlocked) to 55kWh at a price of course...could you charge the 40kWh battery to 100% since it is actually a 55kWh battery? It would be cool if you could.

Thanks,

Kal

 

[JeffK]

Yes, if it's really a higher capacity battery then you can charge to "100%" with no worries.

 

[Frank99]

Well, I don't know for sure. Does Tesla limit the battery at the fully charged end, or the fully discharged end?

With your example 55 KWH battery limited to 40 KWH, Tesla could choose to keep the battery in the 0-40 KWH range, so a 100% charge would only be 40KWH and the battery would be happy. They could choose to keep the battery in the 15-55KWH range, so a 100% charge would by 55 KWH and the battery would be slightly irritated. Or they could choose the 7.5-47.5 KWH range, so a 100% charge would be 47.5 KWH (about 86% full), and the battery would be fine.

I haven't seen any information about how Tesla chooses to do this on the MS-60, so your guess is as good as mine.

 

[Model 3]

I haven't seen any information about how Tesla chooses to do this on the MS-60, so your guess is as good as mine.

It has been confirmed from CAN-reading that the current TMS60 (and TMS70) use the first method, so that car can be safely charged to 100% on a daily basis. If the same will be true for any potential future battery-limited TM3 is yet to be seen.

 

[Saghost]

I seriously doubt that your basic assumption will come true - that in a mass produced car where Tesla is fighting for every scrap of profit margin they'll give you 25-50% more battery material than you're paying for.

Having said that, if they were to, you're likely correct. Tesla has twice delivered software limited models, and in both cases they appear to have chosen to limit the top portion, so charging those cars to 100% doesn't have the effect that charging the rest to 100% does.

My bet would be that you have the sizes wrong, too - that the base will be the ~55 kWh pack that more or less matches the Bolt, and the optional pack will be a 75 or so.

 

[jbcarioca]

We all need to keep in mind that Model S85 cars have driven hundreds of thousands oif miles without harm when charging every day to 100%. While it is true that li-ion do like to avoid over/under charging the Tesla BMS has pretty much eliminated the overcharge issue, and no harm has been evident on the low end as long as SOC is ~10% or so. The official recommendation remains as it has since 2012, not more than 90% or less than 20% on a daily basis. Nobody should be too hyper about this.

full disclosure: I do go to 100% sometimes, driving offf as soon as I reach 100% but I never go below 20%. So, do as I say, not as I do. Old habits die hard for me.

 

[JeffK]

I believe charging to 100% still negatively impacts regen deceleration when you let off the accelerator pedal. That alone might be a reason not to go all the way to 100% unless you're going on a trip. There's absolutely no need to charge to 100% if you have no intention of travelling that distance. If you find yourself doing that then it's more of an OCD thing brought about by habits formed by poor cell phone and laptop battery life.

(This is assuming you have a charger at home and you're going to plug it in every night anyway)

 

[jbcarioca]

I believe charging to 100% still negatively impacts regen deceleration when you let off the accelerator pedal...

That is a fact, Regen gradually returns as SOC drops below 100%, although I have not noticed exactly at what SOC regen returns to normal levels. This, however, is not a reason not to go to 100% if you really need that last bit of range. It is a rare Tesla driver who needs 100%, and that is usually when towing, in mountains, cold or bad weather, or on long trips. As tesla drivers we are lucky. Every other BEV needs 100% for most normal driving so the question of using a lower SOC never even arises for them.

 

[LectrikPower]

I would like to know what the battery voltage is when the car says "0 miles". I have lithium batteries for RC planes and the lowest you want to discharge them to is 3.7v per cell. Given that Tesla's recommendation is 90%-20% for typical use it seems like 0% would be close to the 3.7v which is actually about 20% capacity remaining. Going much lower can greatly reduce cell life. Or is it closer to actual 0% when you get to 0 miles?

Can anyone confirm this?

 

[JeffK]

I would like to know what the battery voltage is when the car says "0 miles". I have lithium batteries for RC planes and the lowest you want to discharge them to is 3.7v per cell. Given that Tesla's recommendation is 90%-20% for typical use it seems like 0% would be close to the 3.7v which is actually about 20% capacity remaining. Going much lower can greatly reduce cell life. Or is it closer to actual 0% when you get to 0 miles?

Can anyone confirm this?

The Tesla battery management system handles all of this for you. You really don't have to think about it.

0 miles is not going to be 0%. (Give the people at Tesla some credit.)

It's an 8 year unlimited mile warranty on the battery and drive unit, therefore it's in their best interest to maintain battery life.

 

[LectrikPower]

The Tesla battery management system handles all of this for you. You really don't have to think about it.

0 miles is not going to be 0%. (Give the people at Tesla some credit.)

It's an 8 year unlimited mile warranty on the battery and drive unit, therefore it's in their best interest to maintain battery life.

Thanks Jeff, I assure you I'm not worried about it. Just curious as to what their 0mi voltage is. 20% is a lot if capacity. I understand they are not stupid I'm just wondering what their margin is.

 

[JeffK]

Thanks Jeff, I assure you I'm not worried about it. Just curious as to what their 0mi voltage is. 20% is a lot if capacity. I understand they are not stupid I'm just wondering what their margin is.

Supposedly one of the older models (85S) kept 6 kWh for anti-bricking and another 5 kWh for below 0 reserve.

 

[Model 3]

Supposedly one of the older models (85S) kept 6 kWh for anti-bricking and another 5 kWh for below 0 reserve.

According to CAN-bus reading it is 4kWh anti-bricking. What is below 0 and usable differs from car to car from time to time, and should not be counted on.

 

[Booga]

I seriously doubt that your basic assumption will come true - that in a mass produced car where Tesla is fighting for every scrap of profit margin they'll give you 25-50% more battery material than you're paying for.

The way Tesla views it is the way Amazon views the Kindle - people will spend more later. If you have a small battery pack, Tesla is betting that you will want to unlock the additional power at some point later. And even if you don't, as long as a certain portion of users do, it'll work out just fine.

 

[Chopr147]

I'm not sure tesla will be giving many options like this on the 3. What I mean is the software limited S 60kwh is a great deal with the 75kwh battery. So many S buyers like me did not bother purchasing the 75 because it makes no sense given the charge rates. The difference was 15 miles more for $9000. This of course is assuming the 60 -100% charge and the 75 - 90% charge.
There is a looooong thread on here all about the charging rates for the 60 and 75.
Tesla is mute on the issue because they want to sell the 75kwh, but the word is out. Don't bother!
The 75kwh S's sold were the inventory ones at the end of the 3rd quarter. Before that it was a small percentage ( A guess going by this forum)

 

[Saghost]

The way Tesla views it is the way Amazon views the Kindle - people will spend more later. If you have a small battery pack, Tesla is betting that you will want to unlock the additional power at some point later. And even if you don't, as long as a certain portion of users do, it'll work out just fine.

That's definitely the financing angle they approached it with. However, I suspect they didn't anticipate just how many people would choose the 60 over the 75 - I assume that's why the X60 went away so quickly.

But what makes sense to drive demand for a $60k car being sold in record numbers with a 20% gross margin is unlikely to make sense to drive demand for a $35k car with hardly any margin and a year or two of orders already booked.

I don't see any reason for Tesla to throw that money out the window - especially since the cost of the extra battery may be about the same as their profit margin on the base car...

 

[Chopr147]

Agreed

I am curious though what battery options will be and which one for the $35,000 model 3
If it's 55kwh, will that be a 60kwh battery? The 3 will have a new battery composition so it's all a guess at this time.

 

[david_42]

Agreed

I am curious though what battery options will be and which one for the $35,000 model 3
If it's 55kwh, will that be a 60kwh battery? The 3 will have a new battery composition so it's all a guess at this time.

Well, I suspect we will know in about 3 hours.

 

[Saghost]

Agreed

I am curious though what battery options will be and which one for the $35,000 model 3
If it's 55kwh, will that be a 60kwh battery? The 3 will have a new battery composition so it's all a guess at this time.

All a guess, as you say.

I don't think Elon will allow the 2016 Bolt to beat the base 3, but the 3 will likely be more efficient. Given that, I think the 55 is a reasonable guess for the base (and in line with the tidbits Elon's thrown us.)

The unveiling projection showed an 8 module pack. My personal theory is that this is the big battery, and the small battery will be a 6 module version with either the front pair or the rear pair removed (whichever leaves them closer to a 50-50 distribution.) This would imply that the big battery is somewhere around 75 kWh...

 

[Model 3]

Agreed

I am curious though what battery options will be and which one for the $35,000 model 3
If it's 55kwh, will that be a 60kwh battery? The 3 will have a new battery composition so it's all a guess at this time.

I do not care much for the actually size of the battery, What I care about is the range. 55kWh is a reasonable guess, but is it 55kWh usable or total?