Speak EV - Electric Car Forums banner

1 - 19 of 19 Posts

·
Registered
Bmw i3s 120ah 2019
Joined
·
15 Posts
Discussion Starter · #1 ·
Apparently charging battery up to 80% is good for battery life.
Is there an option to stop charging at 80% automatically in i3?
 

·
Registered
Joined
·
2,322 Posts
It is worth bearing in mind that cell balancing is required from time to time and this is only managed by the BMS when the battery is at 100% SoC.
 

·
Registered
2020 BMW i3S 120Ah BEV
Joined
·
659 Posts
I've heard the phrase "when the battery is at a high state of charge" but I don't know if this necessarily implies 100%, 90%, 80% or whatever. It's certainly true that charging the car to 100% periodically isn't a big deal. Maybe I might aim to leave it at 80% if I knew I wasn't going to touch the car for a week or more, but otherwise .. not worth worrying about.
 

·
Registered
Joined
·
825 Posts
All the manuals, literature and anecdotal evidence support charging to 100%. The only time I have thought that partial charging would be helpful is if I had been on a long trip and a full charge would take me outside of the 4 hour Octopus off-peak rate. A partial charge would allow me to stop and use the second night off-peak rate. Anyway, you can’t do it with the car and would need a timer on the charger. I could of course set my alarm for 4.30 am, get up and switch off the charge with the app!
 

·
Registered
Joined
·
44 Posts
My old Nissan leaf (1st gen) Had a feature that only charged to 80%. I believe their battery was susceptible to a high state of charge degrading the battery faster. the i3 seems to be fine.
 

·
Registered
Joined
·
2,322 Posts
I know that opinions are divided on this subject but it is worth bearing in mind that BMW only warrants the battery for 8 years, and the warrantied percentage is based on the usable charge not the full battery capacity. it follows that if BMW is going to pay up, the total battery capacity has to fall a lot more than 30%. By not charging up to 100% each time, you might well be prolonging long term battery life which I accept is of no consequence for those on a PCP or who change their cars every three years.
 

·
Registered
Joined
·
825 Posts
I know that opinions are divided on this subject but it is worth bearing in mind that BMW only warrants the battery for 8 years, and the warrantied percentage is based on the usable charge not the full battery capacity. it follows that if BMW is going to pay up, the total battery capacity has to fall a lot more than 30%. By not charging up to 100% each time, you might well be prolonging long term battery life which I accept is of no consequence for those on a PCP or who change their cars every three years.
I am not sure that there is any evidence to support that view whereas there is empirical evidence that rapid chargers do reduce battery life. The Battery Management System (BMS) is designed not to over stress the batteries and to charge to the optimum. What is beyond doubt is that if you only charge the car to 80% and you then need to go on a long journey at short notice you won’t have the full range available.
 

·
Registered
Joined
·
2,322 Posts
I am not sure that there is any evidence to support that view whereas there is empirical evidence that rapid chargers do reduce battery life. The Battery Management System (BMS) is designed not to over stress the batteries and to charge to the optimum. What is beyond doubt is that if you only charge the car to 80% and you then need to go on a long journey at short notice you won’t have the full range available.
As I said, opinions are divided. Whatever you do, it is unlikely that BMW will ever have to pay up.

 

·
Registered
Joined
·
193 Posts
There is a very good summary with real data !!! here What can 6,000 electric vehicles tell us about EV battery health? | Geotab

TLDR A current model I3 will typically exhibit 0.9% loss per year but that includes data from cars in hot countries which show typically 3 times greater degradation. For all car types charging DC increases degradation but only significantly for cars in hot countries, age and climate are more important than duty cycle. The article mentions the 80% idea but does not support it with data.
 

·
Registered
Joined
·
825 Posts
There is a very good summary with real data !!! here What can 6,000 electric vehicles tell us about EV battery health? | Geotab

TLDR A current model I3 will typically exhibit 0.9% loss per year but that includes data from cars in hot countries which show typically 3 times greater degradation. For all car types charging DC increases degradation but only significantly for cars in hot countries, age and climate are more important than duty cycle. The article mentions the 80% idea but does not support it with data.
Interesting but rather short on factual data. I stick with what I said above - charge to 100% so that the full range is available when required.
 

·
Registered
BMW i3
Joined
·
410 Posts
I've heard the phrase "when the battery is at a high state of charge" but I don't know if this necessarily implies 100%, 90%, 80% or whatever. It's certainly true that charging the car to 100% periodically isn't a big deal. Maybe I might aim to leave it at 80% if I knew I wasn't going to touch the car for a week or more, but otherwise .. not worth worrying about.
I’ve seen 80% and 85% mentioned, so tend to charge ours to around 85/90%.

We also have an ICE so in the unlikely event that we had an emergency requiring range beyond that available in the i3 I’d take that!

My view is that that “Always Be Charging” (and to 100%) is put out there to keep things nice and simple for the punter, to ensure that cell balancing happens and so that the maximum range is always available.

From the link mentioned I’d agree with this:


I know of no reason why the Samsung SDI battery cells that BMW uses should be any different from any other Li-ion cell in this respect. It's an electrochemical fact that a cell at a high charge level is more reactive than at a lower charge level. This increased reactivity leads to the acceleration of destructive, non-reversible side reactions that degrade a cell.

By not allowing its cells to charge to 100%, BMW has reduced, but not eliminated this problem. BMW must have calculated that by limiting full charge to 92-95% of the actual full charge, this degradation will be slow enough that few battery packs would need to be replaced under warranty due to capacity degradation exceeding 30%.

Those who lease their i3's would not be affected significantly by such degradation. However, those of us who have purchased our i3's and plan to keep them past the expiration date of our battery packs might be significantly affected by capacity degradation unless we proactively manage our battery packs. I typically charge to an indicated 90% and then charge fully just prior to departing if I think I'll need full range. To accelerate the battery cell charge level balancing process, I try to charge fully monthly and then allow our i3 to remain at full charge at least overnight.

If my battery pack management results in a loss of usable capacity due to battery cell charge imbalance, this could be fixed by allowing the battery pack to remain at full charge for longer periods. This is preferable to losing usable capacity due to degradation that is permanent and cannot be fixed except by replacing battery cells.
 

·
Registered
BMW i3
Joined
·
410 Posts
As an aside, why would the likes of VW say this if charging to 100% is fine?


Three golden rules for more range

It is relatively easy to keep your high-voltage battery well maintained. If you adhere to the three golden rules then you have already done the most important thing to maintain a high range for the vehicle.

1. Please do not charge the vehicle to more than an average of 80% during daily short-trip usage.

2. If the vehicle is not moved for more than 12 hours it should be charged between 30 and 80% of capacity.

3. To fully charge the vehicle (100%) use a charge timer in the charge manager and then drive off immediately after charging is completed.



Perhaps they handle cell balancing differently and/or at a lower SOC but seems sensible to me.

Also says to try and keep it between 40 and 80% in the winter!
 

·
Registered
Joined
·
825 Posts
As an aside, why would the likes of VW say this if charging to 100% is fine?


Three golden rules for more range

It is relatively easy to keep your high-voltage battery well maintained. If you adhere to the three golden rules then you have already done the most important thing to maintain a high range for the vehicle.

1. Please do not charge the vehicle to more than an average of 80% during daily short-trip usage.

2. If the vehicle is not moved for more than 12 hours it should be charged between 30 and 80% of capacity.

3. To fully charge the vehicle (100%) use a charge timer in the charge manager and then drive off immediately after charging is completed.



Perhaps they handle cell balancing differently and/or at a lower SOC but seems sensible to me.

Also says to try and keep it between 40 and 80% in the winter!
Yet BMW tell you to fully charge and do not give you the option to partially charge through the car computer. Not sure how many wall chargers have timers; certainly mine doesn’t and it was the one originally recommended by BMW.
 

·
Registered
BMW i3
Joined
·
410 Posts
Yet BMW tell you to fully charge and do not give you the option to partially charge through the car computer. Not sure how many wall chargers have timers; certainly mine doesn’t and it was the one originally recommended by BMW.
We have economy7 so I tend to have a car timer set for 3 hours in that slot and plug in when it gets down to about 50%, which will bring it back to about 85/90% (I only charge at 3.6kW)
 

·
Registered
2020 BMW i3S 120Ah BEV
Joined
·
659 Posts
VW came out with an electric car a full 7 or 8 years after BMW started selling the i3. They get to learn from other's mistakes.
 

·
Registered
Joined
·
2,322 Posts
What owners do with their EVs is up to them. As I have posted before, it seems to me that BMW is not expecting many battery warranty claims. It is though worth noting that the warranty is based on 70% of the usable battery capacity. It follows for the warranty to kick in on a 120Ah BEV the battery capacity has to fall below 26.53kWhs (70% of 37.9) which equates to a total loss of battery capacity of 37.2% over 8 years.( based on 42.2kWhs total)
 

·
Registered
BMW i3
Joined
·
410 Posts
What owners do with their EVs is up to them. As I have posted before, it seems to me that BMW is not expecting many battery warranty claims. It is though worth noting that the warranty is based on 70% of the usable battery capacity. It follows for the warranty to kick in on a 120Ah BEV the battery capacity has to fall below 26.53kWhs (70% of 37.9) which equates to a total loss of battery capacity of 37.2% over 8 years.( based on 42.2kWhs total)
Yes seems pretty unlikely it’d drop that far even if you did your best to abuse it.

Hadn’t realised that they extended the mileage allowed (to the same as the USA):


Interesting that they claim none have been replaced:

“…Until now, no high-voltage battery of a BMW i3 has had to be replaced due to premature aging.”

Being generous maybe they mean in Europe, as at least one has been in this thread:


Also interesting to see that some cars at around the 70% threshold mysteriously received a decent bump in capacity after a trip to the dealer.
 
1 - 19 of 19 Posts
Top