Battery Life Optimization

[SSL]

There is lots written about optimizing range, but I haven't seen a discussion about how to maximize battery life.

When I took delivery of my car in Sep 2014, I had trouble with the level 1 charger. MB service told me to get a level 2 charger and to cycle the car between 25% and 100% charge.

When I spoke with Customer Service, I was told in no uncertain terms that there are no memory issues with the high voltage battery. It can be run down to 0%, or charged from any remaining charge, and charged to any level including 100% as often as the owner wishes without any impact on the battery's expected life.

When I read Tesla forums and talk to Tesla owners, they are adamant that battery life will be lengthened by cycling the charge from 35% to 85%; that is, charge it when it reaches 35% and only charge it to 85%. However, with about 15% of the B-class' battery held in reserve for the range extender, the 35% minimum charge is probably too high.

Am I the only one who wonders how to maximize the battery's life to 100,000 miles and beyond? Has any one gotten reliable advice from a trustworthy Mercedes engineering source?

 

[tom]

People in the Tesla forum are correct. If you own your electric car you don't want to keep your battery at 100%, at 80% would be much better.

It is all explained in this video (but video is over one hour long):

https://www.youtube.com/watch?v=pxP0Cu00sZs

Jeff Dahn, in the video, is an expert in testing EV batteries. He just signed a 5 year contract to have his team work with Tesla.

If you leased your electric car then you don't care, just keep it at 100% all the time and give the car back to MB at the end of three years, and let the next owner worry about it. That's what I did with my leased LEAF.

 

[tom]

Some more info on Jeff Dahn and Tesla:

http://my.teslamotors.com/forum/forums/dalhousie-researcher-dr-jeff-dahn-collaborate-tesla-motors

http://www.dal.ca/news/2015/06/17/charging-onward--dahns-next-move-marks-first-canadian-university.html

 

[Stretch2727]

I recently watched the entire video and read up on other sites. It has changed my behavior with both my car and cell phone.

A few take aways:

1. High temps will age the battery faster.

2. The higher the charge the more quickly the battery will age. Below 80% the benefit is minimal.

3. Cold is actually good for storage, but bad for operation of the battery.

4. Very low charge has a trigger point failure.

What I do for each of the above points:

High temps will age the battery faster.

1. Keep the car in as cool an area as possible. Garage, shade, indoor parking, etc. Do no drive it hard in hot weather (90 degree +) until the cooling system has had a chance to cool the battery. The battery will self heat on discharge/regeneration so before you do drive hard let the battery cool in hot weather. The car will actually limit the output, that small e-cell gauge on the right of the instrument cluster if the battery is hot.

The higher the charge the more quickly the battery will age. Below 80% the benefit is minimal.

2. Don't charge the car unless you really need it. Try to keep the charge at a lower %. The 80%-25% percent rule from the Tesla forum is probably good.

Cold is actually good for storage, but bad for operation of the battery.

3. Same thing as hot, don't drive hard until the battery has a chance to warm up. I am not sure how the B-class functions in the cold but my Focus would prompt to plug in the cold to keep the battery marginally warm to be ready for operation. If you are not using the car the cold will reduce the aging of the battery. The car will also limit the output (that small e-cell gauge on the right of the instrument cluster if the battery is too cold).

4. Very low charge has a trigger point failure.

4. I don't think there is anything to worry about here. The car is well protected from the lower charge failure point on the car. This is not so much degradation but catastrophic failure if the batteries reach a certain low voltage. The only concern maybe if you leave the car in storage for an extended period (months) as there could be a very slow loss of charge. Ideally you don't want to have it fully charged either (point #2 above) but you may want to plug in if you cannot check the charge on a regular basis.

The car is really designed so you really do not have to worry about the items above. As someone else mentioned regular charge is only 77% of the battery capacity. You could ignore all the items above and the battery will age slowly and meet the warranty requirements. Car companies design for worst case and they know most people do not want to have to think about these type of operational limitations. Also, the car design is very robust compared to some other electric cars with the low % of battery capacity being used and the battery thermal management system it has.

For those that don't mind a few minor adjustments, the above should marginally improve battery life.

 

[tom]

Thanks Stretch!

It been a long time since I viewed that video. Is it true that not much harm is done as long as one does not keep the battery at 100% charged for an extended period of time? For example, do the Extended charge, and then immediately go on the road. Did Jeff Dahn say that in above video?

 

[bcurious]

A few take aways:

2. The higher the charge the more quickly the battery will age. Below 80% the benefit is minimal.


2. Don't charge the car unless you really need it. Try to keep the charge at a lower %. The 80%-25% percent rule from the Tesla forum is probably good.

I think that MB has already handled this battery trait by not enabling the 100% charge capacity in the default charge sequence. Requiring the user to put the charging system into 100% charge mode before charging the battery (and requiring the purchase of that function in the case of pre-2015 models) limits the full charge capacity to below 100% unless specifically desired by the user.
Not charging unless you really need it is, I think, foolish. At any rate, it isn't safer for the battery that way.

 

[Stretch2727]

Yes if you watch the video it is really:

Time X Charge Level = Aging.

Under 80% charge this is negligable but it does have a small effect. Yes, MB has really taken care of this by only allowing the battery to charge to about 80%.

He mentions storing a lithium ion battery at 20% charge in a refrigerator since 1999 and it has not degraded...one at a higher charge did degrade.

There is also the cycling effect which will also age the battery...kind of hard to avoid if you want to drive the car.

As far as not charging, during the week I have a 12 mile round trip to work. I have stopped charging during the week as I really don't need it. Even if I head out at night during the week it is usually just a few miles. On Thursday or Friday night I will charge fully as on the weekend we tend to take some longer trips. So on average the battery is staying at a lower charge level than if I charged every night.

 

[GGV]

Stop worry, do driving

At current technology pace, in 5 years you battery will be considered ancient, regardless of charge state

 

[Stretch2727]

Stop worry, do driving

At current technology pace, in 5 years you battery will be considered ancient, regardless of charge state

Agreed this is why I leased.