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Healthy Battery Practices
September 7, 2014
8:10 pm
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Jim Hindson
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Lithium-Ion Batteries – Long Term Battery Health – September 2014

This summary of information is based on available references to the performance of Lithium-Ion batteries. Specific Lithium Ion battery chemistry and anode cathode composition vary between manufactures but the basic characteristics of Li-Ion batteries are very similar.  This summary is not intended to be an authoritative reference, but is a summary of readily available information. If there are any errors, omissions or suggestions, please advise.

If there is a conflict between the manufacturer’s recommendations or other articles on Lithium-Ion battery health then the appropriate references should be consulted. To avoid warranty issues, in the case of a conflict, the manufacturers’ recommendations should be followed.

The suggested practices are listed, followed by a more in-depth explanation and listing of references as to the scientific basis for the suggested practices.

A) Critical Battery Management Practices

1)    Do not leave the vehicle stored for extended periods (days/weeks) plugged in

2)    Do not leave the vehicle plugged in with the charging timer on after the vehicle has been charged if the vehicle is not going to be used before the next timed charge. 

3)    Do not store the vehicle with a 100% charge. The optimal charge for storage for Lithium-Ion batteries is 30-40% (the opposite of Lead Acid and Nickel-Cadmium batteries).

4)    Follow the manufacturer’s specific guidelines for extended cold weather storage

5)    Do not run the battery down to 0% charge

6)    Do not store the vehicle in  extremely hot or cold temperatures[1]

B) General Good Practices

1)    For daily use, charge the vehicle to 80% [2] unless your planned upcoming trip requires a higher or 100% charge.

2)    Do not regularly “top up” the battery charge from 80% to 100%. It is better to charge more frequently and run the charge down to 20% then charge back up to less than 80%.

3)    Avoid (close to) full battery discharges

4)    When not using the vehicle for an extended period (a few days or more) do not leave it plugged in. Leave the vehicle parked with a 30-40% charge (the opposite of conventional batteries).  As an extra precaution, turn the charging timer off[3] during this period of inactivity.

5)    Avoid storing the vehicle in full-sun conditions.

6)    Avoid excessive periods with Eco Mode Off (Sport Mode On) where the battery may experience higher temperatures due to higher power demands.

7)    Whenever possible use Level 2 charging[4]. Avoid constant use of Level 1 (trickle charging) or Level 3 (440 Volts DC) fast (quick) charging. Especially avoid multiple quick charges at higher battery temperatures.

8)    Start to charge the battery at a low battery temperature. Set the timer (if so equipped) to charge the battery in the middle of the night rather than at the end of the work day or after an extended drive cycle, when the battery temperature may be elevated.

9)    Ensure that the vehicles tire pressure is to specifications

C) Additional Battery Health techniques - for Wannabee Hyper Milers (Geek alert)

1)    When feasible, operate the vehicle in lower charge ranges and depth of charges. For example if a 40% charge is needed for daily use, run the battery between 30% and 70% charge each day rather than between 20% and 100% over two days

2)    Cut the battery highest charge off – at 75% rather than 80%

3)    Avoid trickle charging and fast charging altogether

4)    Avoid parking the vehicle for extended periods in full-sun conditions


Lithium- Ion Battery Health

It should be noted that most, if not all, manufacturers have included allowances for these characteristics in their battery designs and recommended operating practices. If the manufacturer’s recommended practices are followed, it is expected that the vehicles will have the service life indicated by the manufacturer.

However, a basic understanding of the reasons behind the operating recommendations and simple daily techniques to maintain and improve battery health may extend battery life beyond the published manufacturer’s guidelines.

The biggest factor in the degradation of Lithium Ion batteries is a buildup of a layer of solid film on the anodes of each battery cell. A thin film is initially beneficial as it prevents reactions between the anode and the electrolyte, but as the film builds up over time, it degrades battery capacity and performance.

The main factors that can affect Li-Ion battery health are:

Temperature
High battery temperatures reduce battery life by increasing the rate of the buildup of film on the anode and degrading the electrolyte. Areas with temperate climates (such as Victoria) are ideal for electric vehicles. Battery temperature can be increased by ambient temperature, or battery charging or rapid discharging through aggressive driving or loading through elevation increases or higher vehicle (cargo) weight.

Some manufacturers deploy liquid thermal battery management systems (Tesla, GM Volt) and some do not (Nissan Leaf).  The addition of active liquid battery thermal management systems represents a trade-off between battery design and performance and vehicle weight, complexity and cost.

Voltage
Charging Lithium Ion cells to higher voltage levels decreases battery life by increasing the rate of the buildup of film on the anode. Individual Lithium battery cells have a limit of 4.2 volts per cell. Above 4.2 volts, the cell experiences a significant loss in cycle life and can represent a safety hazard. Cell cycle life increases significantly below 4.2 volts and is extended dramatically when voltage falls below 3.9 volts. This operating limitation is the origin of manufacturer’s suggestions to charge the vehicle up to 80% for regular use to extend battery health. Manufacturers also include a safety factor insofar as “100% charge” does not mean that the cells are charged to the 4.2 volt cell upper limit.

Depth of Discharge (DOD)
Cycling the Li-Ion battery on large charge/discharge cycles reduces battery life. Large charge discharge cycles can invoke Lithium Ion battery’s two main enemies – high temperature and high voltage. It is better to have multiple 45% charge cycles from 25% to 70% than single charge discharge cycles of 10% to 100%.

Charge rate (C)
Charging the Lithium Ion battery above or below the optimal charge rate has a long-term impact on battery life. Although less important that temperature or voltage, the rate of charge (C) has an impact on battery capacity fade. C is the current necessary to charge the battery in one hour. For example, the research indicates that for a higher number of battery cycles a C rate of 0.5 (12 kw) may be optimal for the Leaf. Therefore higher charge rates (440DC) and lower charge rates (110V) may be suboptimal.

References

1)    How to Prolong the life of Lithium-Ion Batteries  http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

2)    Battery Capacity Loss http://www.electricvehiclewiki.com/Battery_Capacity_Loss

3)     Why Do Lithium Ion Batteries Die?

4)    Nissan Leaf Owners’ Manual (2013)  https://owners.nissanusa.com/content/techpub/ManualsAndGuides/NissanLEAF/2013/2013-NissanLEAF-owner-manual.pdf

Footnotes:
[1] Consult vehicle owner’s manual
[2] The Tesla and Nissan Leaf have screen settings that will limit the received charge to 80% - refer to owner’s manual
[3] If so equipped
[4] Applies to the Leaf and probably other vehicles. The “sweet spot” charging rate for the Leaf is 12kw/hr. Generation 1 Leafs have a Level 2 of 3.3 kw/hr, Generation 2 Leafs have a Level 2 of 6.6 kw/hr.

Compiled by Jim Hindson, September 7 2014

September 7, 2014
11:24 pm
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Fred Wissemann
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Thank you Jim. I am the proud owner of a Nissan LEAF having traveled over 40,000 Km in almost three years. 

I use my energy until I am down to 30-40 and re-charge to  about 135 - 145 Km.

My battery capacity is still fine. The battery warranty is good for 8 years.

I think I might upgrade my battery after 8 years and use some of that money I saved to increase or double my range.

I heard at our coffee chat TESLA will release a replacement battery for the roadster that will have a 600 mile range. Wow! 

It will cost about $5500 to replace a LEAF  battery and TESLA is trying to get it down to $2400 with their new factory in Nevada. $100 per KW/h

Enjoy your EV 

September 7, 2014
11:32 pm
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Fred Wissemann
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By James Strickland

Many of these points are not generally true of lithium-ion batteries, rather they are specific to the Leaf.  The advice, for example, to not leave the car plugged in, is exactly opposite to what Tesla advises.  The advice to not use "Level 3" charging is at odds with what Tesla advises, which is that there is no limit on Supercharger use.  But then, the Tesla battery is temperature-controlled, and much larger.
 
 

I would agree that avoiding depleting the battery to near empty is unwise, not just for battery life but for your own peace of mind.  Not charging to 100% regularly is wise, but you should do so when you think you might need to.  Otherwise, I would advise not obsessing over your battery's state of charge.  It's not worth the anxiety relative to what little effect it might have on long-term battery capacity degradation.  And I really don't think we should be advertising to the world that owning an EV is complicated and anxiety-inducing, because it really isn't.

btw, saying that you shouldn't charge at 440V DC seems nonsensical to me, since charging *is* DC at the voltage required to make current flow into the battery.  When you plug AC into the car, it is being rectified into DC to charge the battery!  The battery sees absolutely no difference between a charger (rectifier) inside the vehicle and one outside the vehicle (e.g. CHAdeMO).  Both will be applying the required voltage, generally in the range 350 to 400V, depending on state of charge, to cause current to flow into the battery.  All that matters is how much current is flowing into the battery.

 
September 8, 2014
9:58 am
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Jim Hindson
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Thanks for the feedback. Good point about leaving the Tesla plugged in, it loses 1% charge per day on the main battery if left unplugged. Perhaps this is caused by different approaches to battery management when unplugged. Preserve the main battery by disconnecting the 12V (Leaf) or preserve the 12V by retaining a trickle charge from the main battery (Tesla).

Does anyone have experience if the Leaf loses charge on main battery when unplugged? I only have one instance of leaving Leaf for 7 days and experienced no main battery discharge.

Excellent point - the Tesla (gold standard) has no published issue with repetitive fast charges and most likely because of the liquid battery cooling system. This appears to manage the temperature issue but the 80% charge limit acknowledges the effect of higher voltage on battery health

It would appear that the issue with charging at 440 DC is related again to temperature. as the Leaf does not have a liquid cooled main battery When charging at Level 2, the charge rate to the battery is about 8 times slower (4 hrs vs 30 minutes) hence generating less heat than quick charging. This could explain the temperature difference between charging with the inverter (Level 2) or direct DC charging (Level 3) and the reason Nissan notes the battery health impacts of repetitive fast charging.

You make a good point about increasing anxiety about owning an electric vehicle but at least within the current owners, the case might be that the more information that is available, the better - particularly if it avoids problems. 

September 12, 2014
5:16 pm
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Rolf Oetter
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I guess some of the confusion comes from how actively the batteries are managed by th car's computer. In general Jim's recommendations are correct, unless the battery management system takes care of these things for you. For example the default maximum charge for a Tesla if 80%. This means the battery cells stay way under the "critical" cell voltage. The great thing with the Tesla is that the normal range is much more than what you need for your daily driving. Only for the odd long trip will you set the car to fully charge your batteries. After a few days the Tesla will default back to the maximum of 80%. 

Many lithium batteries get killed (have been killed) because people take their old experiences and trasnfer them to Lithium batteries. Leaving a laptop always plugged in is one of them. Many people plug their electrical bicycle in and let it sit for days in the garage. Not good for the batteries. 

I have installed lithium iron phosphate on my boat, and I have to "force" myself not to charge the batteries full all the time. With lead acid before that is what you had to do to keep them healthy. The urge is still there even though the knowledge says not to do that.

The Tesla has 16 micro-processors actively monitoring the battery, including cooling and heating to keep them well tempered. 

Going on long holidays requires some preparation with an EV. With my Tesla I will set the charge parameters to 50% and limit the charger to 10A, just so that any problem in the house cabling will not lead to burning wires. With a Leaf I would use a Christmas Light timer and have it come on once a day for about 10 minutes, mainly to keep the 12V battery charged. I would also start of with a half or more empty battery so it does not sit fully charged for extended periods.

July 17, 2017
7:50 pm
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Horence
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That's a professional guide to teach us how to fix the trouble about battery practices. Before reading this post, the more that I know about battery is how to charge camera battery with 150w power inverter from bestek. Now I have acquired how to use this charger in safe way. Easy to connect this charger with car cigarette lighter charger outlet. Then you can charge any tool that you want. Maybe you can learn more details about this charger on bestekmall. Hope this tip is useful to you. Best regards. 

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