Charging question

[user 688]

On weekends, when I am using my B-Class for short errands and not commuting, is it preferable not to charge it every time and just draw the battery down? Is there some reason I should avoid more charging cycles, or do Lion batteries not care?

 

[wtzouris]

I was thinking the same thing today, it's probably less wear and tear on everything if you don't top off to 100% multiple times a day (like I do) and just charge once a day or maybe even once every two days. But I don't think the batteries care - you are charging them to 80%. I'm on a three year lease that I would consider extending another year or so. There is not much harm in anything short of DCFC which we don't even have on the car.

 

[GlennD]

I always charge at L2 40A. I usually wait until the charge meter is down to 75%. Once a month I go to the TRW swap meet that is 39 miles away. That is the only time I push the extra charge button. It is likely it is not needed but the extra charge gives me warm fuzzy feelings.

 

[JeffRay]

Agree with prior posts that it should not matter unless overusing the Range Extender (which I don't have). I charge every day if I am at work place with 110 outlet. It gets me through a regular work week unless I am taking a side jaunt to Citifield to watch the Mets or out to LGA or JFK. I follow the ABC rule. Even if there is a hit on the back end (I am leasing), it limits my range anxiety to an irregular occurrence.

 

[oilerlord]

Tesla designed the battery to take a lot of punishment which is why the battery comes with an 8-year / 100,000 mile warranty stipulating no more than 30% degradation. If you're leasing the car, I wouldn't worry about it...plug it in when you get home regardless of battery % remaining. I just bought mine used (with about 6000 miles on it) and want to keep it for the long term so I'll be doing my utmost to take care of the battery. Lithium ion batteries don't like:

- Extreme heat
- Extreme cold
- Being stored for long periods at 100% charge
- Being deep cycled (i.e. driving to turtle / charging to full on a regular basis.

I've read that keeping the car's state of charge between 30-70% is ideal but probably isn't realistic.

 

[wtzouris]

The fact that they stated the warranty covers over 30% battery degradation at 100k miles means that it is unlikely the degradation will be anything close to that. (They don't want to pay for a new battery!) I would think 15-20% degradation at most at the 8 year/100k mile mark. But seriously, a standard charge only gets you to 80% (ACTUAL STATE OF CHARGE) anyway, so I wouldn't worry. I'd rather use the car from 30% to 100% (On the dash) than draining it lower than 30% on the dash on a regular basis. in fact, I always use range charge in winter for 65 mile trips to avoid getting too low (Under 20% SOC) on the dashboard.

 

[ECG]

FWIW - previous owner of 2014 RAV4 EV. New owner of 2016 B250e as of two days ago.

Charging - I charged my 2014 EV everyday, with extended range option selected for 3 years. Battery never experienced degradation entire time we owned the car. Some days we charged it from 2% capacity left, some days with 90% capacity left. This was wife's commuter car, and a lease.

After just two days of the b250e, I can tell you Mercedes got into the electric car market as an afterthought. Many of the standard features I had on my RAV4 are nowhere to be found. Hell, I cant even tell the car when I want it to charge - what kind of nonsense is that??

Anyway - from 3 years of experience with the RAV4 with Tesla battery and drivetrain, the only fear I'd have of using the range extender everyday is if I purchased - oh yeah, and with the RAV4 EV range extender is an option that you turn on or off - none of this turn it on EVERY time before you charge the car. Lots of nonsense like this with the Mercedes.......at least it looks really nice inside.

 

[user 738]

ECG - I'm with ya. I just moved from my 2014 RAV4EV to a 2016 B250e also. Same thoughts.

I just pre-ordered one of these to solve the charging schedule issue, as well as the ability to start and stop charging from my smartphone:

https://emotorwerks.com/store-juice...smart-ev-charging-adapter/category_pathway-23

I just hope they start delivering soon.

 

[TheStig]

If you own the car, or intend to buy it out at the end of the lease I'd say unless you need the range for a longer trip don't charge unless below 70%, even better 50%. Like any other lithium battery there is a finite number of charge cycles before capacity begins to degrade. It won't fall off a cliff like a cellphone battery does after 2 years, but at some point a high number of charge cycles will catch up to you (or the next owner).

Also, I don't get the feeling charging from something like 80% to 100% all the time after short trips is efficient from a power consumption or cost perspective. The SOC increase slows considerably as the pack gets near full. An hour of 10Kw charge yields a lot more SOC% starting from 30% than it does from 75%. I'll make up some numbers here but an hour of charge might get the SOC from 20% to 55%, a 35% increase. That same hour from 75% to 100% yields 25% but pulled the same amount of power from the wall and money from your wallet.

 

[oilerlord]

The more I drive the car, the more I realize that ~100 miles is a TON of range for me. I rarely drive more than 40 miles in a day, so I don't plug it in unless the SOC is under 60%, and unplug it when the charge hits ~90% indicated (if I remember to unplug it). I figure that an indicated SOC at 90% only uses 25.2kWh out of the total 36kWh battery capacity - or only about 68% or so. This is probably much ado about nothing, as a "full" charge only uses 80% of the battery, but I would like to see my B turn over 100,000 miles with minimal battery degradation. It makes sense that a lower number of charge cycles is probably better in the long term.

ECG: You had your Rav for 3 years and report no battery degradation...did the dealer test the battery and provide the results, or did you test the battery on your own? Also, how many miles were on your car when you returned it?

 

[leousa]

I charge mine back to 100% every time I can. The reason is because battery management system should still keep cells in the battery package charged at around 80%. The meter that you see on the display just telling us that 100% of the cells are charged back.
Then, when you are driving it again the system should use next cells in line, and keep the ones that was just used until next time it cycle all battery package.
Remember, you battery is not a singe cell. It is a package of around 2,600 individual cells managed by the special controller.

 

[vin]

If you own the car, or intend to buy it out at the end of the lease I'd say unless you need the range for a longer trip don't charge unless below 70%, even better 50%. Like any other lithium battery there is a finite number of charge cycles before capacity begins to degrade. It won't fall off a cliff like a cellphone battery does after 2 years, but at some point a high number of charge cycles will catch up to you (or the next owner)

Not all charge cycles are equal... here's a decent read on the subject.

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

"Similar to a mechanical device that wears out faster with heavy use, the depth of discharge (DoD) determines the cycle count of the battery. The smaller the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses. Partial discharge on Li-ion is fine. There is no memory and the battery does not need periodic full discharge cycles to prolong life. The exception may be a periodic calibration of the fuel gauge on a smart battery or intelligent device."

Still have a '14 RAV4 EV, been charging it 1x-2x/day, typically doesn't get below 70% charge. After 33 months and 32,000 miles, I'm still getting 110-122 miles range after charging to full (not extended). After an 85-mile trip (maybe once/week) it shows about 25% charge left. No apparent degradation yet.