Information needed about ev battery

Goudy

The battery management system will help with what others are saying. As suggested, you are over thinking things a little when the management system is doing the thinking for you already.

There will be a difference between total battery capacity and usable battery capacity, a sort buffer zone at the top and bottom end of the charge/discharge cycle to help protect the battery.

The in car state of charge reading will reflect the management system and not the total capacity. This means if the buffer is for example 10%, the in car charge reading will show 100% at 90% total battery capacity charge. Same for discharge, if the in car monitor says 11%, it's actually protecting the battery and it will have 21% charge.

You can't access these buffer zones though, they are programmed into the cars software to extend the battery's life.

So your car might have 87kWh of usable battery but the actual battery pack will be kWh's bigger, like 91kWh.

The car's software will also be programmed to help extend battery life by altering the state of charge based on current levels within the battery. There will be a sweet spot built into the software where is will charge at full charger rate, but as the battery recharges it will slow the rate of charge. This is why is takes longer to charge the last few % of usable battery compared to say the middle %.

Of course you can still short charge to 80% and recharge at 20% (of usable capacity) but there's a trade off. By doing this you are obviously increasing the number of times you charge it and thus the number of heat cycles the battery will go through.

Where as charging it from near empty to full usable capacity in one go reduces the amount of total recharges and heat cycles.

QrizB

Of course you can still short charge to 80% and recharge at 20% (of usable capacity) but there's a trade off. By doing this you are obviously increasing the number of times you charge it and thus the number of heat cycles the battery will go through.

Sorry but that's a complete red herring.

Goudy

https://forums.moneysavingexpert.com/discussion/comment/82112723#Comment_82112723

If so, perhaps you should explain.

If your battery gives a range of say 200-250 miles and you do say 600 miles a week, that's 3 charges.

If you are only utilising 60% of your battery (between 20% and 80%), that's a range of 120 miles so that's 5 charges in total.

So you put the battery through an extra 2 charge cycles you don't really need to. That's nearly 100 extra charges a year.

We know you can never charge to 100% of the total battery capacity or discharge the battery 100%, the battery software management won't allow you. So what are the benefits of all these extra charge cycles? The battery management software is already doing this short charge for you. All you are doing in introducing extra charges that come at a cost to the battery life.

QrizB

If so, perhaps you should explain.

I explained earlier in this thread, but to address your specific example:

If your battery gives a range of say 200-250 miles and you do say 600 miles a week, that's 3 charges.

Yes, 600 miles on a 200 mile range battery is three cycles.

If you are only utilising 40% of your battery (between 20% and 80%), that's a range of 80 miles so that's 7.5, so 8 charges in total

8 charges, but not 8 cycles. It's still only 3 full cycles.

So you put the battery through an extra 5 charge cycles you don't really need to.

Nope, still only 3 cycles.

So what are the benefits of all these extra charge cycles?

There are no extra cycles.

Goudy

But you can't give an EV a full charge anyway, they are all only part charges but every time you start to charge a lithium ion battery, you force lithium ions to move through the electrolyte from cathode to anode and that causes oxidisation of the cathode.

The total battery capacity is larger that the usable battery capacity.

Your in car display is showing 0-100% but that is equating to something like 15-85% already of the total battery capacity. Your 20-80% charge is in effect something close to 35-65% of the total batter capacity.

In real life you aren't really going to totally flatten a battery (even if you could, but you can't, it won't let you. The car will power down before it flattens the battery completely).

More often that not you will put it on charge at the lower end of what the in car display is telling you. So if you run it down to 10% on the in car display, you can add to that the 15% or so it won't use in the battery.

Now the software won't allow you to fully charge the battery no matter how much you leave it on charge. It will only ever charge to 80-90% of it's total capacity.

So why would to charge it more often? I know why and it's not what everyone thinks.

There are EV's that have been "Fully" charged using mainly fast chargers that show very little drop off over hundreds or thousands of miles.

It's correct, a battery like this will last longer if charged and discharged in this way and the evidence for this is very very strong, but get this, it's not a special secret only few know.

You can't seriously suggest that only a few know and that doesn't include any of the car and battery manufacturers? They know, which is why the car's batteries and charging system have had extensive researched and developed and is why they have already been programmed it to do this. Which means you don't have too.

But everyone's fears of EV battery life has caused people to want to do something themselves, plus there were people panicking about the number of chargers. So having owners think there is something they can do to extend the life and anything that got people off the on street chargers quicker was always going to be welcome by everyone in the industry.

QrizB

every time you start to charge a lithium ion battery, you force lithium ions to move through the electrolyte from cathode to anode

It's not just when you start a charge. You're moving lithium ions through electrolyte continuously from the start of the charge to the end of it. That's how charging works.

There are EV's that have been "Fully" charged using mainly fast chargers that show very little drop off over hundreds or thousands of miles.

Which is good news for everyone, as it suggests that car manufacturers have got their battery chemistry / geometry / management systems right. For an EV battery that's good for 1000+ cycles, it's likely the battery will outlive the car even with fast charging.

For example, this calculator suggests that for Mrs QrizB's e-UP! with a 32kWh NMC battery, 16.5kWh/100km and driving 12000km/yr, the battery will last 25 years. A quick look on Autotrader shows that there are a few 25-year-old VW Lupos still around, but I'm sure most have already been scrapped.

anything that got people off the on street chargers quicker

I would suggest that the main thing that gets people off the DC chargers and onto 7kW home AC chargers is the price of public charging.

And I'm glad we now seem to be agreeing that charging daily rather than weekly isn't going to reduce battery life by adding extra cycles.

lordmountararat

EV batteries are much more resilient than was thought in the past. Mine has just come up to five years old and I had the battery checked last week. It came out at 93.3%, so degrading at 1.32% a year. You might want to be aware that EV 12 volt batteries can fail suddenly; they don't usually give signs of degradation in the same was as those in an ICE vehicle. Some EV specialists suggest changing the 12 volt battery every five years to be on the safe side.

chuffinnora

I have a PHEV and initially thought the same, how can I extend the EV battery life. After a bit of research I quickly come to the conclusion life is too short. The manufacturers have built all the safety and mgmt margins into the software. I charge to 100% every day and often use all of it every day. Only time I make an effort to keep the charge within a threshold is when away on holiday for a week or more.

The little difference you can make is not worth the hassle. Would you take the same approach with an ICE? EV batteries and ICE engines have long life these days.

matt_drummer

https://forums.moneysavingexpert.com/discussion/comment/82113638#Comment_82113638

How many cycles does your battery have on it so far?

As you charge it every day and often use all of it you can probably have a stab at how long it will last.

1,500 cycles would be just over four years if there was one full cycle a day.

chuffinnora

It doesn't matter to me, it lasts as long as it lasts. A family member is still running the same model at 125000+miles with some degradation, but nothing major. Its there to be used not preserved.

There is a cost to running a car. There's a warranty and there are replacement parts as and when required. If I didn't use the EV part then I'd be using fuel more. The point is I'm not going to fret over how many cycles I charge or how much its used.