Ideal charging behavior

[jhs_7645]

I know Tesla recommends charging every day, and charges to only 90% capacity when not in range mode, but I was wondering if that pattern is ideal for battery life. I drive on average about 30 miles per day. So, conceivably, I could go a few days without needing to charge.

So here's my question, disregarding the fantastic advice to always have the car charged up because "you never know", what is the ideal SOC (state of charge) to keep the Model S at, in order to maximize battery life?

 

[ElSupreme]

I generally think discharging your battery at low SoC is probably worse than having your battery sit at 90% SoC. I imagine that the Tesla recommendations is probably close to ideal.

 

[kinddog]

I generally think discharging your battery at low SoC is probably worse than having your battery sit at 90% SoC. I imagine that the Tesla recommendations is probably close to ideal.

correct. i think a lot of research went into Tesla's recommendation to always have it plugged in if possible. they have a LOT of interest/incentive in the battery lasting as long as possible.

 

[childressmd]

... so...

Is everyone plugging every night and letting it charge to standard charge every day?

 

[ckessel]

... so...

Is everyone plugging every night and letting it charge to standard charge every day?

No, I tend to plug it in every 3rd night or so. I use around 40 EPA miles per day, so I end up plugging it in when it hits about 50%. Sometimes I do it more often, just depends on if I feel lazy when I get out of the car or not.

 

[Doug_G]

... so...

Is everyone plugging every night and letting it charge to standard charge every day?

Absolutely. Been doing it for years with the Roadster, and am continuing that with the Model S.

 

[ElSupreme]

... so...

Is everyone plugging every night and letting it charge to standard charge every day?

Yep plug it in every time I park it in my garage. Even when I know I am going out later. Only actively charge between 11pm and 7am (super cheap electricity) unless I know I need more charge.

 

[djp]

... so...

Is everyone plugging every night and letting it charge to standard charge every day?

No, I generally plug in my Roadster when it drops to 25% SOC and charge to a maximum of 50% SOC (except when I need more range). I have zero battery degradation after three years.

LiOn batteries like to be stored at a low SOC and used at a high SOC. If you're doing more 'storing' than 'using' then a low SOC is better for battery life.

The following shorten battery life and should be avoided:

• Sitting at a high SOC (the Roadster has a "Storage Mode" that keeps the battery at roughly 20% SOC)
• High temperatures, especially combined with a high SOC
• Deep charge cycles
• Drawing high current at a low SOC
• Charging when the battery temperature is below freezing

Both the Roadster and Model S have battery management safeguards to avoid all the above, including active cooling/heating for the battery pack and limits on charging, power and regen. LiOn batteries are happiest when stored in a cool place at a constant 20% SOC and never charged or discharged. This doesn't make for a useable car though and Tesla engineers have done a great job of trading off battery life for usability by avoiding the extremes. You'll be fine using the defaults, and if you want to baby the battery just avoid the five points above.

 

[mknox]

Is everyone plugging every night and letting it charge to standard charge every day?

Yes, without fail.

 

[FredTMC]

No, I generally plug in my Roadster when it drops to 25% SOC and charge to a maximum of 50% SOC (except when I need more range). I have zero battery degradation after three years.

LiOn batteries like to be stored at a low SOC and used at a high SOC. If you're doing more 'storing' than 'using' then a low SOC is better for battery life.

The following shorten battery life and should be avoided:

• Sitting at a high SOC (the Roadster has a "Storage Mode" that keeps the battery at roughly 20% SOC)
• High temperatures, especially combined with a high SOC
• Deep charge cycles
• Drawing high current at a low SOC
• Charging when the battery temperature is below freezing

Both the Roadster and Model S have battery management safeguards to avoid all the above, including active cooling/heating for the battery pack and limits on charging, power and regen. LiOn batteries are happiest when stored in a cool place at a constant 20% SOC and never charged or discharged. This doesn't make for a useable car though and Tesla engineers have done a great job of trading off battery life for usability by avoiding the extremes. You'll be fine using the defaults, and if you want to baby the battery just avoid the five points above.

very interesting strategy. How many miles do you have on your car? I typically don't charge up to a full standard charge daily. But I do charge everyday. Your success is validating that I shouldn't charge up more than I know I'll need for the next day.

I so only complete charging right before I intend to use the car for my morning commute (~ 20 mi)

 

[Bipo]

My laptop (Sony VAIO) have two modes to prevent battery degradation:

- Stop charging at 80% SOC (intended for use unpugged)
- Stop charging at 50% SOC (intended for use plugged)

As I always use it plugged to the grid, I chose the latter, so the battery always stays at 50% SOC. A few months using that and the battery life is optimal: When I need to travel I charge up to 80% and it lasts for four or five hours. I have never charged it up to 100% (let's call it "range charge") because I never needed it.

So, if I were you, I'd charge the Model S to always keep the SOC between 40% and 60%

 

[jerry33]

Standard charge every night. No reason to do anything else unless you are going to need a range charge the next day.

 

[Oyvind.H]

Seems as if ideal charging behaviour is to keep the battery around 20-50% SOC and always charge after use so the cycles are as shallow as possible?
I.e. if your commute is 40 miles total per day you use about 14-15kWh. Leaving with 50% SOC, this will run the battery down to 30-35% SOC. Then recharge immediately to 50% when you get home, and you`ll have optimal storage SOC and as shallow cycle as possible. Shallow cycling, avoid heat and no 100%SOC/0%SOC seems to increase battery life a lot! The sources I have found points to shallow cycling being far better than full cycles. In other words, plug in all the time, but interrupt charging at low SOC

 

[NigelM]

Why try to second guess? There's sophisticated software and systems to maintain your battery pack at an ideal state and Tesla engineers have always said plug in every night. That goes for Roadster and Model S.

 

[Oyvind.H]

Why try to second guess?

Because we can

Jokes aside, think of mobile phones (i.e. iPhone). iPhone charge to "100%" and keep the battery at 100% until you unplug. Mobile phones don`t need to have 10 years battery life. 3-4 years is good enough. And often you will need 100%, so the phone charges to 100%. For the phone manufacturer it does not matter if the battery only lasts 4 years with usable capacity. After 3-4 years most people swap for a new one anyways.

For Tesla it probably doesn`t matter if users experience 1,5 or 2,5% degradation per year. It`s well within what to be expected, and everyone is happy. So the engineers prioritize usability, but with some limits. The battery in a Tesla does not need to last 20 years. 10 years will do just fine, so Tesla can program for the best user experience with i.e. 10 years as a life expectancy goal with 75% capacity.

According to what I`ve read, cycling around 40-50% is better for battery life than 80-90%. The difference is probably not big (maybe 1% degradation instead of 2% per year, wild guess), but it only matter to those of us who have way above average interrest in batteries. And to Tesla it does not matter as their system preserves battery life good enough!

Limiting to 40-50% SOC would generate a lot of bad press ("You only trust your battery warranty by seriously limiting range on ar regular basis? It`s just a 100 miles car?"). So the answer is 90-93% SOC max on standard charge, as it is the best compromise for a car.

Maybe I can reduce degradation from 2% to 1% by keeping the battery around 50% SOC? Several sources imply that I would benefit from keeping the battery at a lower SOC (but the most important thing is shallow cycles! Always plug in after use!). I would not recommend that most people try to keep the battery around 50% SOC (and I probably won`t either), but I like exploring the subject.

 

[MikeC]

After reading a similar thread last month, I started to only charge to 200 rated miles or so, trying to keep a lower SoC. Problem was, sometimes I would forget or need the full rated range the next day, so it meant I was doing deep discharge/charge cycles instead of shallow ones. I figured this offset any gain I had from keeping the SoC lower. If I was going to not drive for a week or two (hope that never happens!) I'd keep it at around 50%. Reading that most Roadsters have negligible deterioration after several years was also reassuring.

 

[traxila]

For those of us with short commutes (~30miles / day) and access to both 240v and 110v, which amperage is best for the battery? Does it work better to trickle in over 10 hours or top off after one hour?

Thanks.

 

[Oyvind.H]

And now Tesla offers the ability to set maximum charge between 30-100% instead of just 90/100%.

 

[gaswalla]

He means with the next upgrade to 4.5

 

[Oside2lv]

I charge my MS daily to 80% charge I thought....just reading that its 90%. However, like others have posted I believe that Tesla has a vested interest and spent a lot of research hours I determining efficiency and longevity. I'm gonna stick to charging mine daily after my 50 mile day.