Worrying drop of battery and range below 25%

[jammamon]

Hey guys, I went to work yesterday and when I arrived the car had 22-23% battery. Six hours later when I got back to the car it showed 18% and after just 12km of modest driving (average speed 30km/h) it reached only 10%. The estimated range fell during that day from ~120km to only 50km, while driving only about 22km. Consumption was normal the whole time at ~15 KWh/100km.

Keep in mind I used no air conditioning, neither did I leave the lights on when I parked.

I charged the car and now it behaves normal again. I was just wondering what is your experience when the battery falls below 20%. It was the first time I've let it drop that low and it surprised me.

 

[tsedge]

You need to:

1. Regularly charge to 100% and let the car balance (weekly if you have the SR, monthly with the LR). This is to equalise the cells and make the battery behave predictably.

2. Let the car discharge to 10% and then charge to 100%, every 3-6 months. This is for accurate battery calibration.

If you are not doing these then you may see suddenly drops at low SOC because the battery is out of balance or calibration. This seems to be more important on the SR than the LR.

 

[jammamon]

Thanks for the input. When you say "let the car balance" what exactly do you mean other than charging it to 100%?

 

[fnegroni]

This is my battery (SR) balancing once it has reached 100%: it will continue charging at very low power for about 20 minutes to half an hour after reaching a stated 100%.

 

[dsr]

To make quite sure the battery does balance completely, I play safe and leave the car ‘charging’ for an hour once it gets to 100%. Hoping nobody is going to tell me that this is too long ?

 

[benflugel]

You can tell in the app if it is balance charging. It still shows the car as charging but the charge rate will read something like 0.1kw

 

[Alb]

The BMS will take care of charging optimisation so leaving it for an hour or more is not an issue.

 

[OriginalBigAl]

You can look up, discharge rates of EV batteries. A quick overview is LFP batteries have a flatter more linear discharge rate but near lower SOC tend to fall off a cliff, which is what you are experiencing. NMC batteries discharge less linear but give a longer single charge life and tail off less dramatically. Obviously its a lot more complicated than this and others will give a better description. Balancing will help to steady the figures but its just a matter of getting used to your own car and its particular vagaries and where ever possible charge up before reaching 20% . Because of this drop off at lower SOC the GOM range estimator is all over the place with its constantly changing predictions .

 

[Rolfe]

This is why I am bloody paranoid about balancing my car's battery, and doing the long charge regularly, especially just before a long trip when I know I'm going to drive it down low.

It's working. I'm away from home at the moment and have driven long mileages on several days. I've got into the habit of choosing the charger I'm aiming for and programming it in to Android Auto. I watch the miles ticking down on AA beside the remaining range ticking down on the driver's screen, and have to say the car has been faultless, allowing me to ease off my right foot if the margin of error looks a bit tight, and press on when I can see it's all good.

I balanced the pack on a public destination charger yesterday afternoon and I'm off home after lunch. Heading confidently for Annandale Water, 143 miles away at motorway speeds. I have no qualms because my experience has been entirely positive.

Balance a few times and do at least one <10% to 100% charge (always on AC) and I'm confident your car will start to behave like mine.

I'm being told that one should leave the car for an hour or two at <10% before starting the long charge, although I don't know how important that is. I am also persuaded (by people using terms like "hysteresis curve" and "coulomb counting") that it's important to do the long charge in one continuous operation, even if you do have to use a bit of peak price electricity in the process.

When you balance all the time and do your long charge, you can do this with confidence. (Me at Annandale Water. Might have gone a bit faster than ABRP estimated.)

 

[pjmmk]

When you balance all the time and do your long charge, you can do this with confidence.

I think my heart would be pounding by the time I reached my destination!

 

[Rolfe]

It was fine. I started off with over 40 miles in hand, but I knew that wouldn't last. First 65 miles it did last though, as the A65 isn't a fast road and at two points, believe it or not, I was following horse-drawn gypsy caravans - on one occasion for quite a few miles. On to the M6 northbound and I had the cruise control set at the point where cops are unlikely to take any notice, and just drove on. Gradually the miles in hand (the difference between Android Auto and the GOM) reduced to about 10 miles. I gave Caliban a bit of a breather (OK, 70 or so) and saw the whole thing stabilise - I wasn't losing any more headroom. Then there was quite a long stretch of roadworks with a 50 limit and my headroom grew again during that.

I flipped the ACC back up a bit once I was through the roadworks and the headroom started decreasing again. However I was getting close enough to the service station that I didn't see any point in pulling back until I got to the slip road. The GOM did drop by a couple of miles as I was getting close, but nothing to worry about.

The point is that if I'd been worried at any point I could simply have slowed down. If I'd run out of headroom then 60 or 65 would have given me more, and that's still not slow for motorway driving.

The ability of EVs to hypermile quite spectacularly at low speeds really should prevent any actual disasters so long as you don't behave like an idiot. And so long as you can trust your car's readouts. Which I maintain you can in the SE SR, so long as you balance frequently and do the long charge at the recommended intervals.

I probably took on a bit more charge than I needed - I got home on 18% and 33 miles range. The reason for that is that despite knowing that my range doesn't decrease from Wells of Tweed almost to Broughton, I can't quite bring myself to start with less range than the distance home. In fact I was on 39 miles range at Wells of Tweed, and still on 39 miles range as I approached Broughton. It's 30 miles from Wells of Tweed to home, and I only dropped 6 miles range. It's a steady downhill where you can seldom exceed 50 mph, so the GOM, which was originally imagining I'd still be belting up the motorway, compensated gradually to account for the change in driving conditions.

 

[unbornidentity]

This is why I am bloody paranoid about balancing my car's battery, and doing the long charge regularly, especially just before a long trip when I know I'm going to drive it down low.

It's working. I'm away from home at the moment and have driven long mileages on several days. I've got into the habit of choosing the charger I'm aiming for and programming it in to Android Auto. I watch the miles ticking down on AA beside the remaining range ticking down on the driver's screen, and have to say the car has been faultless, allowing me to ease off my right foot if the margin of error looks a bit tight, and press on when I can see it's all good.

I balanced the pack on a public destination charger yesterday afternoon and I'm off home after lunch. Heading confidently for Annandale Water, 143 miles away at motorway speeds. I have no qualms because my experience has been entirely positive.

Balance a few times and do at least one <10% to 100% charge (always on AC) and I'm confident your car will start to behave like mine.

I'm being told that one should leave the car for an hour or two at <10% before starting the long charge, although I don't know how important that is. I am also persuaded (by people using terms like "hysteresis curve" and "coulomb counting") that it's important to do the long charge in one continuous operation, even if you do have to use a bit of peak price electricity in the process.

Yep, I don’t think it’s anything to worry about so long as you run it down to <10% then fully charge every 6 months and charge to 100% once a week or so.

LFP batteries don’t have much of a voltage change between fully charged and flat. If you don’t fully charge it frequently and near discharge it occasionally, it’s just guessing the state of charge. If a cell gets low the whole pack reports the lowest level.

The whole 20-80% thing is still better for battery life but if you do that most of the time then the BMS won’t be able to accurately guess the state of charge

 

[Rolfe]

Euan McTurk doesn't think 20-80 is even relevant with LFP batteries, and considering that even NMC batteries seem to do pretty well even if that rule isn't followed, I'm not worried.

I made sure to do a <10% to 100% charge a couple of days before I set off, and as I had plenty opportunities to charge to 100% on type 2 chargers while I was away, I was pretty confident of the accuracy of the GOM.

 

[fnegroni]

Incidentally I’ve just stopped my SR to 90% because I don’t like how when it’s at 100% I get less regen and as I’m in the Peak District for a few days I want as much regen as I can get.

 

[decrep]

Incidentally I’ve just stopped my SR to 90% because I don’t like how when it’s at 100% I get less regen and as I’m in the Peak District for a few days I want as much regen as I can get.

Mine gives peak regen at 93%, (one pedal starts), not that that makes much difference

 

[unbornidentity]

Euan McTurk doesn't think 20-80 is even relevant with LFP batteries, and considering that even NMC batteries seem to do pretty well even if that rule isn't followed, I'm not worried.

I made sure to do a <10% to 100% charge a couple of days before I set off, and as I had plenty opportunities to charge to 100% on type 2 chargers while I was away, I was pretty confident of the accuracy of the GOM.

Jeff Dahn’s research says otherwise but they should last at least twice as long as NMC so still nothing to worry about.

BU-808: How to Prolong Lithium-based Batteries

BU meta description needed...

batteryuniversity.com

 

[tsedge]

Jeff Dahn’s research says otherwise but they should last at least twice as long as NMC so still nothing to worry about.

BU-808: How to Prolong Lithium-based Batteries

BU meta description needed...

batteryuniversity.com

Yes, I have nothing against people trying to optimise but I just use my car as I want to and no signs of any deterioration after 15,000 miles and 14 months.

 

[Rolfe]

Incidentally I’ve just stopped my SR to 90% because I don’t like how when it’s at 100% I get less regen and as I’m in the Peak District for a few days I want as much regen as I can get.

I just let mine go to 100% because it isn't long before the regeneration starts to kick in.

 

[decrep]

we manly do short local trips, and recharge on peak solar, looking at BU-808.
I think we'll be better off staying between 65% and 75%.
But that must increase the number of cycles, so is it an advantage?

 

[siteguru]

It was fine. I started off with over 40 miles in hand, but I knew that wouldn't last. First 65 miles it did last though, as the A65 isn't a fast road and at two points, believe it or not, I was following horse-drawn gypsy caravans - on one occasion for quite a few miles.

Been there, done that.

It's the Appleby Fair coming up.