Will slow charge extend battery life?

Will slow charge extend battery life?

Will be charging my MS S60 overnight on a 14-50 40A socket and don’t need fast charge. If I reduce the rate of charge to say 20A, will this help extend the life of the battery?

BillPlanoTexas | June 18, 2013

I've read that slower charging and minimizing taking the battery to 100% charge (i.e. max range) as well as avoiding taking it to a heavy discharge state will help with its long term life. but until these cars have 10 years on them for real world data, I haven't seen the specific amount of impact those issues have. chances are by the time your battery has a meaningful degradation they will have affordable replacements anyway.

DTsea | June 18, 2013

I would think slow charge would slightly improve charge efficiency (ratio of Wh stored to Wh from the wall) since the heat dissipated by the power feeders is proportional to square of current. So at 40A you dissipate 4 times as much heat as at 10A; 16 times as much as at 10A.

That said I am impatient so I just leave it at 40!

MarkV | June 18, 2013

For what it is worth, I have been charging at 20 amps since early November. Time will tell whether I experience any long term benefit. What I did notice in the dead of winter was that the batteries were still warm when leaving for work in freezing temps and I was not restricted much if at all on the regenerative braking which does happen if the batteries are cold.

mvannah | June 18, 2013

I don't know if the difference between those relatively low rates of charge (compared to a supercharger) will affect battery life, but I have read that when you finish your charge right before you leave in the morning, the battery last longer because the battery is not sitting very long at the higher charge state before you start using it for the day.

Schlermie | June 18, 2013

Someone reported from a recent Tesla TechTalk that one of the battery experts made the following recommendations for optimizing the life of your battery:

1. Keep the battery state of charge around 50%
2. Charge at around 40A
3. Stop charging around 1 hour before you begin driving

RanjitC | June 18, 2013

@Schlermie If 40A is good is 20A better?

Schlermie | June 18, 2013

There weren't many details. The exact quote was, "Charging at 40 amps is optimum."

This information would have a lot more value if the battery lifetime benefits from these habits were understood. If you regularly practice these disciplines for eight years, how is the battery degradation impacted? Does the battery degrade by 20% instead of 25%? 10% instead of 20%? 18% instead of 20%?

Robert22 | June 18, 2013

The recommendation sounds logical but I get a different answer every time I've asked this question since December. Tesla has no current consensus and has offered no uniform recommendation on how to care for these batteries short of "leave them plugged in" as mentioned in the outdated manual. It's puzzling that no effort is being made to educate owners when this is the most costly component of the car and is the most amenable to proper prospective care.

shs | June 19, 2013

Note that "keep in plugged in" is not the same as keep it at max state of charge. The fact that both the car and the manual remind one to restore the charge setting to standard after a max charge, and the more recent slider in 4.5 are indication of Tesla's advice on minimizing battery degradation - avoid max charge unless necessary for long distance travel. I agree it would be nice if the manual was updated to state all of this clearly.

nvjx | June 19, 2013

I don't think anyone at Tesla knows for sure because these batteries are different than the ones in the Roadster so time will tell.

Brian H | June 19, 2013

A field testing engineer told me the battery was almost unkillable; he was amazed at Tesla's engineering/achievement.

justineet | June 20, 2013

This is an interesting -- good -- other words, does fast charging -- especially supercharging -- affect the life span of the battery pack negatively in any significant way??? Reports indicate, NO! That is primarily due to Tesla's innovation to run the battery cells through cool and hot cycles during the charging and operation stages so the battery cells are always at optimum temp range required to extend the life span. Tesla reportedly has proven this in the labs.

But one thing for sure will shorten the life span of your battery pack is leaving your battery in complete or near complete(deep) discharge state for long periods of time. So you should always try to never leave your car in deep discharge state for an extended period of time. Frequent deep discharging is not also recommended. Tesla probably has incorporated a safety circuit to avoid deep discharge state. Still frequent deep discharging is not recommended. Even with deep discharge safety circuit on board, the battery pack might still go below the "safe" discharge level since batteries continue to self discharge on their own at some rate.

Brian H | June 20, 2013


AmpedRealtor | June 20, 2013

I'm a bit bothered by Tesla stating a 300 mile ideal range and a 265 mile EPA range, but then disclaims that charging to that level may negatively impact the longevity of the battery. That seems disingenuous. That would be like Mercedes telling you not to completely fill up your gas tank, because if you do, the tank will get a little bit smaller each time.

I know this is new technology and we are giving Tesla a long leash and tons of understanding because we all want the company and its vehicles to succeed in the marketplace. But I'm still bothered by some of these things.

sia | June 20, 2013


All cars come with some caveats. How about this one:

Luxury ICE cars require using super unleaded gasoline. Are they saying that their car is not as "tough" as a $20,000 car?

carlk | June 20, 2013

@AmpedRealtor Perhaps Tesla can tell us how many range charges is too many. On the other hand the battery warranty does no specify how many range or super charges are permitted. Elon has said you can abuse your battery any way you want, short of burning it, and they will still replace it if it fails.

kback | June 20, 2013

They've also been pretty clear that it's ok to charge to the max for road trips and when needed, but for every day driving it's best to charge to 90% or less. Since I rarely need a max charge(haven't yet,) this doesn't bother me. I guess people who need a car that can frequently go more than 240 miles per day might want to choose an alternative car, for now. Once the 100 or more superchargers are up and running, with possible battery swapping (details tonight,) this won't be much of an issue. I don't feel that Tesla misled me in any way.

AmpedRealtor | June 20, 2013

@ kbackman - I don't feel mislead and I certainly don't mean to leave that impression. I am going in with eyes wide open. I just feel that for electric cars to become a mainstream, the claims will have to hold up with fewer qualifiers and under a lot more scrutiny by people who are not very forgiving.

justineet | June 20, 2013 should not really worry about that. I believe what Tesla is saying is it's not recommended to charge it 100% as a standard mode of operation on a daily basis. And it's perfectly ok to charge it 100% for your occasional long distance travel. So Tesla's claim of idle and EPA miles are quite valid.

Nevertheless, I don't think it's necessary to charge 100% even for long distance travel especially once they roll out the superchargers across the country. 80 to 90% will be more than sufficient even for long distance travel. And 50% or less charge is more than sufficient for your daily city commute in my opinion..Or charge it once 80% every 2 or 3 days depending your average daily often of you drive your cars every day with full gas of tank especially ?? Rarely??

Brian H | June 20, 2013

The last 10-20%, even with the new faster "top end" charging, are generally not worth the time if there's another SC 150 miles away. Depending on how you drive!