The Rules of Model S Road Tripping

The Rules of Model S Road Tripping

I just came across this very informative post on how to do road trips in the Model S over on the TMC site.

"Never, ever hesitate to use 100% Charge. Ever." Wow, really? "A few hours at 100% charge has NO measurable impact on battery pack lifetime, and may actually improve battery pack balance." Any insights into how that (the "balance" improvement) works?

Car t man | 2013年10月30日

Correct. People make ideologies out of simple basic guidelines. Don't charge to 100% just for the hell of it. Do it every time you may need it (way better than to completely deplete the battery) and do it every few weeks, to balance the cells. It is better if you then drive the car as opposed to letting it stand but the vampire load will quickly unload those top few % anyway.

People complicate way too much. Many will cause way more harm to their battery by depleting them completely too often and have a worse experience due to frantically looking for emergency charging options.

notice | 2013年10月30日

I've seen this post as well but it conflicts with any official written instruction from tesla (that I am aware of) and with published specs for similar battery chemistries. Believe what you want, but I for one would like to see authoritative sources for this kind of recommendation - The Tesla manual warns max range charge reduces battery life and makes no suggestion or recommendation for rebalancing. And the reserve at 0 miles will protect against damage on the low end by design (though one should avoid Brodering)

Car t man | 2013年10月30日

Lithium based chemistries don't like sitting at over 90% charge and go below 20% in terms of prolonging battery life. But that is just for optimizing life, not a severe instant hit, if you do it rarely, for short periods, etc.

It is hard to say but at the bottom, the batteries are likely limited at some 10% for driving and 5% before the car goes to protective sleep or turn off completely to save the battery.

Ideally, the car would have top balanced equalized battery modules, with same capacity. The way most manufacturers do it and in a way screw up a bit, is so that the balancing goes on constantly which actually continuously kills the balance. If the cells were balanced only at top, only at range charges, you would only need to balance them once a year for instance.

Because the "meddling" of electronics happens all the time in a Tesla also (as far as I know), that balance is actually being killed every time the battery is being depleted. Lithium cells, especially it same temperature, don't really drift in practice. So the constant meddling of the BMS, even during depletion of battery, is actually a legacy nuisance.

Your rate charge falls because the BMS makes the cells drift, so without an equalizing charge (range charge) some cells are more full than others and those which are less full, become the narrow throat and shorten your range temporarily, until balanced again. It is why you see range increase back to normal if it falls inexplicably in same weather conditions and driving pattern suddenly.

Car t man | 2013年10月30日

back to normal after a range charge.. damn I need to start checkign my posts until an edit function is present

robert | 2013年10月30日

So, if I understand you correctly, one should make a range charge now and then, and then "drive off" the extra charge asap?

It would be nice, if someone from Tesla or Panasonic could amplify on this.


Car t man | 2013年10月30日


yes. Because the batteries can only be properly balanced when fully charged.
Technically, you should only do it for that specific reason (balancing) if your range drops inexplicably. If not, no need. And besides, most do take
a long trip at least once a month, so range charging then would be best.

You don't really need to balance them for the balance itself. As the user, you would balance them, to get back the full range, if you need and use it.

Tesla could make the battery basics more known to users, to spare many from scares about sudden drops in range. Also the part about extreme cold and heat really denting range. People deal with it well. It is the unexpected sudden changes on the dash that scare many and quite unnecessarily.

The cars electronics really shield the batteries from any quick damage very well. You shouldn't worry about that. You won't harm your battery in the first year or two for instance. If something would be wrong, it would be the tech or configuration, not user error. It would be covered under warranty.

robert | 2013年10月30日

Thank you Car t man

Do you have any inside info as to how much one should do for the daily charge? I mean, 50-90% is quite a large span.


Car t man | 2013年10月30日

Under 90% and above 50% since you don't want to regularly deplete to below 30% if unnecessary and also you want to have some reserve. If you really do short distances and charge daily, set it to 80%. Lower states of charge, like 40% are meant for storage in warehouses, for potentially longer periods, like even years. Then that is best. For long term storage.

robert | 2013年10月30日

Thank you, Car t man, and PLEASE don't take this offensively: you do know what you're talking about, I mean, you do have some expertise? I know this comes through as aggressive and impolite, and I don't want that. OTOH I really want to be as nice as I can to my car, and therefore I must try to make sure that the advice I will be following also is the soundest advice. On the advice of Chris elsewhere, I will not sign off with my name (but spent 2 lines instead in trying to explain why, ouch...).

MacDaddyDude | 2013年10月30日

+1 Robert!

Yes, Car t man, I find your explanations helpful and consistent with other things I've read and experienced over the years. Additional information about the nuances of battery chemistry is ALWAYS appreciated!

Mathew98 | 2013年10月30日

Robert, we know who you are.

From you postings, it sounds like you drive quite a bit with your car. Why worry about the charging state when you can set it to 90% everyday and forget about the rest?

There hasn't been any other official statements from TM other than the following:
50-60% charge for long term storage
80-90% charge for normal driving needs
100% max charge for anticipated long trips

The S85 has unlimited miles warranty over 8 years so the battery degradation concern should not be an issue.

You are a busy man and I'm sure you can spend the time elsewhere other than worrying about the charging % for the MS...

BTW, I am thoroughly enjoying the MS to the fullest everyday. I wish I didn't have to run errands with my other two ICE boxes just to keep their 12V batteries from draining.

Car t man | 2013年10月30日

I can understand your concern and can put your mind to ease. This is the best way to treat these batteries. And I have lots of lithium batteries in storage for different projects. Even for my oncomming Aston Martin conversion. Those are stored in a cold basement at 40%. They won't deviate from that in a decade. It is a very stable chemistry. It is outside elements such as BMS systems or other vampire loads that discharge them..

I think that degradation at 100% charge and 30C is between 20 to 25% annually.
It means if you store them completely full and at high temps, they will by about 20% in one year just sitting there. Lithium batteries don't want to be full and warm for periods. Especially when both.

For short periods, it is not an issue. You don't need to build your life around them. Have them adjust to yours via Tesla's user interface.

gill_sans | 2013年10月30日

@Car t man, thank you for the informative explanations. Now I think we'll go for 100% (rather than 90%) next time we drive to LA.

Car t man | 2013年10月30日

Go for it. It is best if you set the charge so it finishes just before your departure, if possible, but again, not necessary at all. Just so you know the mechanisms behind it and in which direction to lean, when possible.

If you use your cars daily and on long commutes and have unscheduled drives often, stick with 90% as the daily setting. If you do shorter drives, with few unscheduled drives, set it to 80%. Thats it..

gill_sans | 2013年10月30日

> If you do shorter drives, with few unscheduled drives, set it to 80%.

Sorry if I missed a previous explanation on this, but what's behind your recommending 80% for daily charging vs 50 to 62%? (Just that the long-term range effect of charging to 80 or 90% vs 50-62% is negligible?)

jat | 2013年10月30日

I agree in general with these recommendations, though there are some differences between lithium battery chemistries and it is possible that the particular NCA chemistry used by Tesla has some slight differences.

Car t man | 2013年10月30日


if you do trips that short, to cover them in such a small consumption
section, then 50-62% is great. Not a large difference but if it is
that constant, it is a tiny bit better. If it isn't constant, go
to 80%...

surprisingly, this is very constant across li ion chemistries.

what was found though is that it is better to charge more often
to get smaller discharges than more rarely and have deeper cycles.
si it is better to charge more often incrementally on a daily
basis for instance.

robert | 2013年10月30日

@Car t man
Your comments have set my mind at peace. I have perhaps worried unnecessarily. I will follow your recommendations.
Thank you very much for your time and friendliness!

kback | 2013年10月30日

Car t man - Does the rate of charge have any effect - ie charging at 10-15 amps vs. 40 amps? Some have speculated that charging slower allows the charge to spread more evenly among cells, though I realize this is probably not the right way to say it. Others have said that charging at 40 amps is best for the battery. What's your opinion?

Brian H | 2013年10月30日

The two things to avoid:
Full charge and then leaving the battery sitting for an extended period (weeks, months)
Draining empty (all the way).

Everything else is trivial.

Car t man | 2013年10月31日

Pleased to be putting minds at ease.
Slower rate of charge is always easier
on the battery than quicker. It is less
stressful but then again, these batteries
really are good at high currents.

They can take a hell of a beating. It is almost
more dependent on the battery temperature than
the current itself. If the cells are at 20C,
they can absorb insane currents (hence 135kw
chargers). Towards the end, their temp rises
and that is one of the main reasons for slower
charge towards the end.

The reason 40 amps is suggested over lower rates
like 16 amps is that overall charging efficiency
(basically how much power you draw from your wall socket
and pay for) of a charge is a bit lower then.

It has to do with the fact that the car, when
charging at 16 amps, is plugged in for longer
to be charged and during that entire time,
the car gobbles on power also for all its
systems, as opposed to sleeping instead.
It isn't on a "diet" if it thinks it
isn't necessary. When plugged in, it is
in an all you can eat buffet :)

The battery itself, would prefer the lower
charging current but the cost and power
consumption from your wall socket increase.

Quick charging wears the battery out more quickly,
but Tesla picked the optimal settings so that
the difference is negligent. When you can,
supercharge, when not, go for the 40 amps,
or whatever rate charges the car in time
for your departure.

Brian H | 2013年10月31日

Only owners can be negligent.

Car t man | 2013年10月31日

my mistyping or my auto correct put on notice :)

CarlE_P439 | 2013年10月31日

I've used 100% (Max Range) charging on about 5 occasions (taking trips that are over 300 miles one way) over 10 months. I am not concerned about what effect that may have had on my battery life. I am more concerned about being stranded on the road nowhere near an outlet. Use the Max Range charge when you need it and don't worry about it!!!