Great EV Battery article - good advice

[neal adkins]

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.

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.

Honda seems to imply cell balancing occurs at the top of the cycle and thus recommends charging to 100 percent before driving. That's what I recall reading in the manual. I think You have an excellent understanding of the issue. Thanks for your post Vicking79. I'm down in Southwest Arizona so I need a good plan for hot summer months. What I have been doing is charge to 100 percent. If I don't drive for several hours I just run the climate control remotely some and discharge to around 90 percent . Any advice would be appreciated.

 

[Viking79]

For high temperatures, I am not sure what is the best solution there. Looking at those Blue Energy graphs they are showing impressive cycle life at 55 C (130 F), but I can't read the Japanese on those to know for sure what they were meaning. The car already only charges to 85%, so not sure how much it would help dropping to 90% indicated (maybe 75% SoC). I think not charging fully in high temps is mostly a BEV problem, and not a PHEV problem. The Leaf runs into trouble because the battery chemistry doesn't like being charged to 95% when temps are around 100F or higher and was subject to rapid degradation. That was a problem specific to the Leaf, and not necessarily applicable to other cars.

 

[Pushmi-Pullyu]

Honda seems to imply cell balancing occurs at the top of the cycle and thus recommends charging to 100 percent before driving. That's what I recall reading in the manual.

If I'm wrong on this point, I'd certainly like to know. Do you (or anyone) have a citation from the Clarity PHEV manual about charging to 100%?

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[insightman]

If I'm wrong on this point, I'd certainly like to know. Do you (or anyone) have a citation from the Clarity PHEV manual about charging to 100%?

On page 466 of the Owners Manual it says to fully charge, but doesn't explain why that might extend the battery's lifespan:
To help extend the lifespan of the battery, it is recommended
that you fully charge the battery each time prior to driving.

 

[Pushmi-Pullyu]

On page 466 of the Owners Manual it says to fully charge, but doesn't explain why that might extend the battery's lifespan:
To help extend the lifespan of the battery, it is recommended
that you fully charge the battery each time prior to driving.

Thanks, Insightman! I confess to being puzzled about this. More research needed!

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[RoysHonda]

How much would a level 2 charger decrease battery over time?
I was planning on buying a level 2 charger for convenience, but if I really don't need it, is it better to just stick with the stock charger to extend the battery over its life?

Thanks in advance.

 

[Pushmi-Pullyu]

How much would a level 2 charger decrease battery over time?
I was planning on buying a level 2 charger for convenience, but if I really don't need it, is it better to just stick with the stock charger to extend the battery over its life?

I haven't seen anyone claim that L2 charging leads to shorter battery lifespan. I have seen some plausible claims that it's cheaper to charge with an L2 charger vs. an L1 charger, due to higher efficiency with L2 charging.

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[KentuckyKen]

How much would a level 2 charger decrease battery over time?
I was planning on buying a level 2 charger for convenience, but if I really don't need it, is it better to just stick with the stock charger to extend the battery over its life?

Thanks in advance.

I think @insightman or @Pushmi-Pullyu or somebody posted that even the charge rate for a full 32 Amp Level 2 charger is still below the threshold of being damaging to the battery. Since the PHEV Clarity doesn’t fast dc or supercharge, we really don’t have to worry about this IMHO.

 

[kent335]

I bought my Clarity in California, so I have a 10 year / 150,000 mile warranty on the battery. My plan is to drive it as much as possible, hope the battery goes below the minimum acceptable level prior to 10 years / 150,000 miles, and have Honda replace the battery.

 

[RoysHonda]

Thanks guys! I was thinking about getting a Level 2 charger off amazon for only $369.00. No bells and whistles.....just charges fast.

 

[KentuckyKen]

Aha, I found the post about Level 2 charging rate being too low to worry about. It was @Viking79 in the Honda general forum:

“Yes, we use the L2 multiple times per day at max power. Even at 7 kW it is only 0.4C (charge rate vs battery capacity). This is still slower charging (I think this rate is called "rapid charging"). Typically 1C and above is fast charging, for Clarity this would require 17 kW charging for the PHEV, and even 1C for most battery chemistries is still not much added stress.”

Thanks, Viking!!!

Source:
https://www.insideevsforum.com/comm...ok-to-use-240-level-2-charger-every-day.2940/

 

[weave]

I bought my Clarity in California, so I have a 10 year / 150,000 mile warranty on the battery.

Sigh. I live in one of those 10/150k states (Delaware) but I'll be moving to NOT one of those states (Virginia) long before I could use it. :-(

 

[Ben Washburn]

How about limiting the number of recharging cycles themselves? For example, the car is fully charged, I go to the store and back, and have 39 miles left. No real plans to do anything other than that sort of thing for the next few days--essentially indefinitely because in my case I'm retired. Some days I won't drive at all--or only the mud truck to take the dog swimming.

So I've never read one way or the other, but it just seems to me not putting the car through an 'unnecessary' charging cycle to top off to 47 at all would be better than just recharging it by rote every time I park. The way I drive I can see I would cut the number of times I plug in the car by half or more, and it just seems to me that must be easier on the battery and the cells.

But I really don't know.

 

[Ben Washburn]

Sigh. I live in one of those 10/150k states (Delaware) but I'll be moving to NOT one of those states (Virginia) long before I could use it. :-(

I'm in the same boat. I'm wondering if it would make sense to sell it to a state resident before I move. That warranty by itself must be worth thousands in the right states, especially if you're in that 6-8 year range.

 

[PHEV Newbie]

How about limiting the number of recharging cycles themselves? For example, the car is fully charged, I go to the store and back, and have 39 miles left. No real plans to do anything other than that sort of thing for the next few days--essentially indefinitely because in my case I'm retired. Some days I won't drive at all--or only the mud truck to take the dog swimming.

So I've never read one way or the other, but it just seems to me not putting the car through an 'unnecessary' charging cycle to top off to 47 at all would be better than just recharging it by rote every time I park. The way I drive I can see I would cut the number of times I plug in the car by half or more, and it just seems to me that must be easier on the battery and the cells.

But I really don't know.

Not sure if I'm answering your question but it is generally the worst to charge fully and then discharge fully before your next charge cycle. There is a concept called depth of discharge (DoD) and you want to keep that as shallow as possible. Even though they have a buffer above and below like any EV and PHEV, Tesla recommends that you don't charge higher than 80% for everyday driving. Honda recommends recharging every chance you get. All this is to keep the DoD as shallow as possible. For the best battery longevity, you want to charge and discharge around the 50% point depending on your everyday needs. For example, if you only drive a few miles at a time and have chance to charge in between, charge to 60% and discharge to 40% and repeat. If you drive a bit more, charge to 80% and discharge to 30% and repeat.

More frequently charging for shorter durations do not hurt your battery. If it did, you would be wrecking your battery just by driving because the system is constantly discharging (power to traction motor) and recharging (regenerative braking).

 

[Ben Washburn]

Not sure if I'm answering your question but it is generally the worst to charge fully and then discharge fully before your next charge cycle. There is a concept called depth of discharge (DoD) and you want to keep that as shallow as possible. Even though they have a buffer above and below like any EV and PHEV, Tesla recommends that you don't charge higher than 80% for everyday driving. Honda recommends recharging every chance you get. All this is to keep the DoD as shallow as possible. For the best battery longevity, you want to charge and discharge around the 50% point depending on your everyday needs. For example, if you only drive a few miles at a time and have chance to charge in between, charge to 60% and discharge to 40% and repeat. If you drive a bit more, charge to 80% and discharge to 30% and repeat.

I guess that would be a factor sometimes. I'm more in the case of asking how to handle five miles a day, something like that. Day one I drive five miles and I'm back in the garage with 42 left. Then day two I drive another five miles and I'm down to 37. And so on.

It SEEMS to me it would be better to just let it go down to about 20 miles or so over a sequence of days and not just recharge back up to 47 after every little trip, or even every night, 'just because'. Obviously unless I know I have a longer trip.

 

[PHEV Newbie]

I guess that would be a factor sometimes. I'm more in the case of asking how to handle five miles a day, something like that. Day one I drive five miles and I'm back in the garage with 42 left. Then day two I drive another five miles and I'm down to 37. And so on.

It SEEMS to me it would be better to just let it go down to about 20 miles or so over a sequence of days and not just recharge back up to 47 after every little trip, or even every night, 'just because'. Obviously unless I know I have a longer trip.

You are correct. You should not charge to full, drive 5 miles and then charge to full again. The general advice for storing lithium ion batteries is to charge them only to 50%. The same applies to light usage. In your case, if you know your usage before the next charge opportunity is light, I would charge to 60-70%, drive the 5-10 miles and then recharge to 60-70% again until you know you'll need a lot of miles, then charge fully.

 

[Ben Washburn]

You are correct. You should not charge to full, drive 5 miles and then charge to full again. The general advice for storing lithium ion batteries is to charge them only to 50%. The same applies to light usage. In your case, if you know your usage before the next charge opportunity is light, I would charge to 60-70%, drive the 5-10 miles and then recharge to 60-70% again until you know you'll need a lot of miles, then charge fully.

I'm sure that's true from a battery 'storage' and 'usage' POV--how a battery likes to sit and how it likes to be used. But I'm also thinking on top of that, simply limiting the number of charging cycles the battery goes through would also have a good effect. The fewer times I send electrons pulsing through the system the better it is, regardless of relative charge levels, it seems to me.

Either way, that's what I'm going to do. Not recharge 'just because' until I'm in the low 20s.

 

[Pushmi-Pullyu]

...it just seems to me not putting the car through an 'unnecessary' charging cycle to top off to 47 at all would be better than just recharging it by rote every time I park. The way I drive I can see I would cut the number of times I plug in the car by half or more, and it just seems to me that must be easier on the battery and the cells.

I don't think charging the car for, let's say, 4 quarter charging cycles is any more stressful to the pack than one full charging cycle.

I seem to recall some old advice for the Leaf that you shouldn't charge it if it's above 80% capacity, but I suspect that has more to do with the fact that it's bad to keep the pack continually near 100% charge. With a PHEV, that's less of a concern because a greater percentage of the pack's capacity is used for reserve. As has been noted many times in discussions here, when the car's display says 100% charge, that's not really 100% of the battery capacity. It's somewhat less.

A lot of people say it's best to get into the habit of plugging in whenever you park the car for the night; that will help avoid forgetting to charge it up. I think that's probably the best advice for most Clarity PHEV owners.

Those who want to maximize battery life by using the 80/20 charging strategy (or 70/30 or whatever) might have a reason to take more care about when they do or don't charge, but that's more applicable to BEV owners than PHEV owners.

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