Great EV Battery article - good advice

Ray B

Ray B

Active Member
I learned a lot by reading this article... https://cleantechnica.com/2018/08/26/the-secret-life-of-an-ev-battery/

Some highlights:
  • If the car is sitting in the hot weather a lot (unused), better to have it at low-mid charge level than fully charged
  • To maximize life, the battery management system targets a lower maximum voltage instead of a fully charged state (~4.2V)
  • Best to limit the working range of the battery; for instance routinely work between charging no more than 85% and not allowing it to go below 25%. Routinely going from nil to 100% to nil will shorten the battery life. (Your battery management system does this already by not allowing a true 100% charge nor 0% depletion, but avoiding the full limits is probably also somewhat helpful)
  • Easy on the accelerator; discharging at a lower rate helps maximize EV battery life
 
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So as I understand it...Honda has engineered a buffer on both ends of the battery charge/discharge cycle.

A "100%" charge as indicated by the Clarity is actually only 80% capacity of the battery? Same for the discharge side?

Is my understanding correct?
 
Yes - I think Honda's and all car-makers battery EV management systems do the same thing. Otherwise, the batteries would drop off in performance after ~500 cycles.
 
So no need to be overly concerned about lowering battery life since the Clarity batteries charge/discharge between the recommended percentages recommended in the article.

Correct?
 
David A said:
So no need to be overly concerned about lowering battery life since the Clarity batteries charge/discharge between the recommended percentages recommended in the article.
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Once again, Honda's done a great job, in the Clarity, of producing a car we can simply drive and enjoy.
 
I would say that is a good way to put it... Not be overly concerned.

If you are concerned about lengthening lifespan of the battery as much as possible, then moderation is helpful. So avoid charging when extremely cold, avoid letting it sit for long periods in high heat when it is fully charged, avoid too much rapid discharging, and avoid routinely cycling between 100% and 0% battery levels when practical. Keeping the battery level between 20 and 80% (true state of charge would equate to probably 40 and 70% for a new battery) will promote longer life of the battery. Obviously this could be challenging depending on your daily commute.
 
Ray B said:
I would say that is a good way to put it... Not be overly concerned.

If you are concerned about lengthening lifespan of the battery as much as possible, then moderation is helpful. So avoid charging when extremely cold, avoid letting it sit for long periods in high heat when it is fully charged, avoid too much rapid discharging, and avoid routinely cycling between 100% and 0% battery levels when practical. Keeping the battery level between 20 and 80% (true state of charge would equate to probably 40 and 70% for a new battery) will promote longer life of the battery. Obviously this could be challenging depending on your daily commute.
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Better yet, stop driving, remove the battery and store it in your freezer, then pack the car in Cosmoline (oops, I'm showing my age again).
 
I think people way overthink battery protection. Let the engineers solve those problems. First and foremost drive what suits you.

Clarity only charges to 4.05 V per cell, which is about 85%, and doesn't discharge all the way either.

Cold charging is limited to lower speeds. Very cold discharge will avoid using the battery at all and run hybrid mode.

If the battery gets hot it will also switch to hybrid mode. The Clarity does a lot to protect your battery. Do what is convenient. If you don't need to charge every day, don't.
 
Viking79 said:
Clarity only charges to 4.05 V per cell, which is about 85%, and doesn't discharge all the way either.
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That's pretty good to hear that I don't need to do anything but plug it in and let it charge. What's your source on those numbers?
 
David A said:
So as I understand it...Honda has engineered a buffer on both ends of the battery charge/discharge cycle.

A "100%" charge as indicated by the Clarity is actually only 80% capacity of the battery? Same for the discharge side?

Is my understanding correct?
Click to expand...

I don't know that it's exactly 80% at the top or exactly 20% at the bottom for the Clarity PHEV, but yes.* All EV makers do the same. Generally speaking, larger battery packs (whether it's a PHEV or a BEV) have a smaller percentage reserve at top and bottom, but in most cases the actual kWh reserved tends to be roughly the same.

*I see another comment here claims a maximum charge of 85%; I find that more likely. 15% reserve on the top and another 15% on the bottom is probably closer to what the actual figures are. A 40% reserve seems excessive for a battery pack with as big a capacity as the Clarity PHEV has.
 
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Pushmi-Pullyu said:
I don't know that it's exactly 80% at the top or exactly 20% at the bottom for the Clarity PHEV, but yes. All EV makers do the same. Generally speaking, larger battery packs (whether it's a PHEV or a BEV) have a smaller percentage reserve at top and bottom, but in most cases the actual kWh reserved tends to be roughly the same.
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I hear you...I used the 80/20 to keep things simple. Its the concept that is important to understand.

As long as EV vehicle batteries have an adequate built in buffer...and utilizing some common sense charging protocols mentioned above by several folks...the vast majority of regular folks like myself should be fine with passive battery management.

Good thread and lots of helpful info.
 
David A said:
As long as EV vehicle batteries have an adequate built in buffer...and utilizing some common sense charging protocols mentioned above by several folks...the vast majority of regular folks like myself should be fine with passive battery management.
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I completely agree. I myself have often given advice here about the 80/20 charge/discharge strategy, to extend battery life. That is, for everyday driving, to charge to 80% of what the car's instrument panel says is 100% (even though we know it's somewhat less) and try not to discharge below 20%.

But that's only for those who want to make an extra effort to extend their car's battery life. Some people can get rather obsessed about that, just as there are Volt owners so obsessed with never ever burning any gasoline at all that they have discussions about how to avoid having the gas engine turn on even on very cold days when the car is designed to run the engine to warm up the battery pack.

New Clarity owners should be advised that if they want to make an extra effort to extend their car's battery life as long as possible, then there are strategies to do so. But they should also be made aware that the car is engineered with a built-in buffer to prevent premature battery aging, so if you don't want to worry about it, you can just charge it to what the car's instrument panel says is 100% when you charge the car... which doesn't necessarily have to be every day. (I've seen some older advice that a plug-in EV should be charged to 100% every day, but unless you're frequently in danger of running out of range, that's not very good advice.)
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I disagree with never charging to 100 percent. As a previous hybrid owner and having a battery go bad I can tell what I learned from many people smarter than me. There is a process called cell balancing that needs to occur from time to time. Just like any other battery a cell can and will start to go bad. Others can better explain what occurs. Many people who offer maintenance on hybrid batteries do so by a process of charging/discharging to nurse the battery back to health. What happens is when you never charge the battery to 100 percent is that some cells will be different states of charge and will go to a lower soc than others. So the manual says to charge to 100 percent before driving. That may not be necessary nor practical to do every single time but you should do it regularly so all the cells can balance out. The manual says that the car needs regular exercise just like we do. There is obviously value in all the advice as it relates to charge levels in extreme temps. One other correction is that there is a thread on this forum called clarity battery longevity and a graph showing the actual soc for 100 percent soc and when depleted. I think it's around 94 percent when it shows full charge and 20 percent when depleted.
 
The 94% charge point is inaccurate, someone calculated simply as 4.05/4.20, which is not a valid assumption. 4.05 V represents an SoC of about 85% (maybe as low as 80%) since the 0% SoC is not at 0 V and the discharge is not linear.
 
There's a lot of good information in the article. The worst thing you can do to the battery is to have the battery heated by the environment, fast charging, or fast discharge (Tesla warns drivers that Ludicrous Mode ruins batteries). The article is just providing information so you can decide how to use your car. When I first got the car, I charged overnight for a full charge. During the day, I used the car for multiple errands which depleted the battery to near bottom. Repeat daily. Then I learned that this was the most harmful way to use the car. I now charge to 75-80% between errands and this keeps the charge range between 45%-80% all the time, pretty optimal according to articles out there on batteries. I can do this because I work from home and I realize most people don't have this choice. However, there have been folks thinking that cycling full charge to full depletion is the best way and that's simply not true.
 
neal adkins said:
There is a process called cell balancing that needs to occur from time to time. Just like any other battery a cell can and will start to go bad. Others can better explain what occurs. Many people who offer maintenance on hybrid batteries do so by a process of charging/discharging to nurse the battery back to health. What happens is when you never charge the battery to 100 percent is that some cells will be different states of charge and will go to a lower soc than others.
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This is, unfortunately, a widespread myth on EV forums. Here are some actual facts:

1. It's claimed that repeatedly charging a battery pack to less than 100% and discharging it only partially, creates a "memory effect" which will reduce the amount of charge batteries hold, and that this can be fixed by first discharging the batteries to near-exhaustion and then charging them to 100%. The reality is that this applies only to NiCad batteries, and no modern EV uses NiCad batteries.

2. For cars with NiMH battery packs (not including the Clarity PHEV), some claim that the calibration of the battery pack's instruments (not the cells themselves -- just the calibration of the sensors) sometimes gets out of whack, and it's claimed that you need to fully discharge and then fully charge the pack in order to recalibrate the sensors. Some incorrectly claim that you can "recover" lost capacity -- and thus lost range -- in this manner. (Some call this a "memory effect", but technically that's incorrect, since it has a different cause than the actual memory effect in NiCad batteries.) Even if recalibrating the car's BMS (Battery Management System) will cause it to show a higher range than it previously did, that's still not actually adding to the car's EV range. It's only adding to what the car estimates as its EV range. And even in such a case, those who practice that technique say it should only be done once every 2-3 months, not once every few days.

3. There is no benefit at all to discharging-and-fully-charging for the Clarity PHEV, or other EVs using li-ion battery packs. All that will do is wear out your pack a bit faster.

For those who have even the slightest doubt that everything I've written here is 100% true, please read this discussion thread at the Tesla Motors Club forum. (It's true that the linked discussion is specifically for Tesla cars, which are BEVs, and the Clarity is a PHEV. But both types of cars use lithium-ion packs controlled by a BMS (Battery Management System) which constantly monitors the cells, and I think it's safe to believe that Honda's engineers were capable of competently designing a BMS.)
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Cell balancing is vastly different than memory effect. Cells sometimes discharge at slightly different rates (as percent of SoC) due to differences in internal resistance, etc.

When you charge/discharge over many cycles they can get out of balance. Depending on when the car balances cells, usually after charging or "at the top" the car will charge to a certain voltage then bleed power from the high voltage cells, usually by shunting through a resistor to ground (creating heat) so they are all the same voltage.

This process usually only happens during the last phase of charging.

What happens over time is the car has a low voltage trigger for each cell, if any cell reaches min voltage the battery is dead. The SoC is based on current out of the pack, expected capacity and voltage of the pack.

If cell balancing gets very off it can lead to cells reaching their cutoff voltage early meaning a suddenly dead pack even though it is registering some charge.

Bolt EV had a recall for this, and not charging all the way on a regular basis could lead to the same. It is implementation specific though as balancing could occur if not fully charged. Don't know what Honda BMS does specifically.
 
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