[Lantirn]

Hi PHEV users,

I would like to know the way you charge for optimum usage and minimum long term performance degradation of the high voltage lithium ion battery.

Although many users here say that indicated 100% is not really 100 but less, the actual value will be significantly higher than the popular 80% (known limit for maintaining battery health) if you compare the percentages of net with useable battery kw/h. This means that just charging to 100% will not keep the battery health in good shape long term, unless you lease the car and you opt for fuel minimization.

BMW user guide is clear, charge daily up to 80% for battery health, and if required for range, charge to 100% but close to the departure time. Nothing more nothing less.

Questions arise:

What is better, to reduce the number of charging cycles? Or try to minimize full charges by plugging whatever the state of charge is?

First example from above statement is to depart with 80% and then try to recharge when battery is low again the same day or next day but doing a full charge cycle from lets say 10% to 80% or more.

Second example is depart with 80% and doing a small trip and when back home the battery is 50%. Do you charge immediately to 80% so doing half charge cycle?

What is better? Doing more small cycles more frequently by plugging again and again? Or waiting till the battery is low?

While in full EV vehicles the range 80%-20% can be very easy to manage since the mileage is vastly increased, PHEV considerations are availability of electric range within the same day when replugging, optimization of fuel consumption but also battery health.

So for someone that uses every day only the battery for small commutes, what is better?

I know that in the end its a car and maybe I am overthinking. Some say you should charge it to 100% because it is build for that purpose, or abuse the battery and maybe at the end of the 8 year of warranty you could get a new one if the performance is awful...but I would like to know what you are doing.

At the end, it is a compromise between battery life vs PHEV utilization (with battery abuse to reduce fuel consumption)

[MontyB1]

We charge to 80% each night during the summer as it gives all the charge she needs and we use a slower mains charger that the car came with.

In winter up to 95% due to the far lower range with cooler temperatures and more charge used for steering wheel, heating the car etc. etc.

She puts it to 100% when she goes on a longer journey on the motorway and maintains the charge to use more EV in slower built up areas.

Is the above the right way to manage it, it seems to be working and I suspect also putting less high straight on the battery.
- fast rapid charging is bad too often
- few 100% charges apparently is better
- cool the battery before charging so don’t charge immediately.

However the software is getting better to manage the above, it ramps down the charge before it gets full for example. PHEV BMWs doing really do fast charging either and it’s bigger large EV batteries that can be the issue rather than the PHEV batteries.

Drive it and enjoy it and don’t worry to much ultimately, the car will help manage it all.

[Fish Fingers]

We charge the X1 30e to 100% each time.

Main reasons:
Only 14.2 kWh is useable of 18 kWh (about 79%) so it's a good buffer.

And we often need full range in a day.

Slow charging (AC) is nowhere near as damaging to batteries as EV fast charging (DC).

We get cheap overnight rate electricity (about 25% of day cost), so it makes sense to charge once to full capacity overnight.

I am sure I read somewhere (link on this forum maybe?) that stated in a PHEV it is actually beneficial to charge to 100%.
Edit: found it in this thread

https://u11.bimmerpost.com/forums/sh...highlight=Phev

Our other car is a Taycan and I generally only charge that to 85%.
However, on those forums there are people who ultrarapid DC charge to 100% all the time (no home charging) and have done high miles and the battery is still in very good condition.

So I think you can trust the manufacturers tech nowadays to protect the battery.

Main exception is if we are leaving the cars for long periods (holidays etc) I try and leave them close to 50%.

[Fish Fingers]

In answer to your original question OP.
This was the most referenced post on the other (EV) forum about charging cycles from someone with practical experience at the sharp end of battery technology (tech heavy, but good summary at the end) ...........

I work on satellites that use Li-Ion batteries.

In orbit, we can see tens of cycles a day going in-and-out of eclipse, so maintaining battery health is a critical function since we want these to last for many years in-orbit. While there is numerous different cell chemistries that are used by cell manufacturers, I expect most Li-ion cells to behave similarly from a life standpoint.

While I can't share the actual test report since it's proprietary to the cell vendor, I can share some findings from some of their life testing going through 5000 discharge cycles under various conditions (charge/discharge rate, temperature, depth of discharge):

- Heavy discharge / charge cycles ((C)apicity/2 rates, which would only be ~58 Amps for us - 93kWh battery/800V = ~116Ahr) from 100% to 0% and back caused the biggest degradation - the batteries only lasted <1000 cycles before falling below 80%. While we physically can't discharge at C/2 for more than a few seconds, some of us are likely charging at rates greater than C/5 (23A) regularly.

- Heavy discharge / charge cycles (C/2) from 100% to 60% resulted in a ~10% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 60% resulted in only a ~8-9% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 80% resulted in only a ~5% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 90% resulted in only a 2% degradation after 5000 cycles (yes, double the cycles than the other tests performed, with less degradation).

For the space rated batteries, temperature doesn't look to play a big role on degradation, but does impact how fast we can charge/discharge the batteries, so we tend to keep them cold when not in use (0 degC when battery is fully charged), and 20 degC when charging/discharging (we pre-heat before the eclipse, then the draw on the battery tends to be able to keep it at that temp). During long periods of no battery usage (out of eclipse season), we tend to drop the batteries down <80% capacity for storage.

So, what does that all mean? How frequently you charge actually has little effect on battery life - it's really how much battery you 'use'. You basically get the same degradation for the same amount of battery used - 2500 cycles at 20% versus 5000 cycles at 10% end up causing a 4-5% degradation of the total battery capacity (so equal energy used in those 2 cases). And 2500 cycles at the 40% DoD caused 8-10% degradation of the total battery - also in-line. Thus, the biggest limitation on Li-Ion batteries is big discharges (>80%), and heavy charge/discharge cycles (C/2). I know I've seen other test reports that show data for C and 2C discharge rates as well, but I'm not finding them at the moment.

I believe this is all consistent with what EV owners have seen - you don't want to use the fast chargers everywhere, and avoid deep discharges on the battery (<20%). You can potentially extend the life a little bit by charging at even slower rates - I actually backed my home charger off to 20A because I have no savings having it take 8 hours versus 4 hours over night (and I was occasionally getting overtemp warnings on the charging unit on the hot summer days).

[Swie]

Originally Posted by Fish Fingers

We charge the X1 30e to 100% each time.

Main reasons:
Only 14.2 kWh is useable of 18 kWh (about 79%) so it's a good buffer.

Actually it's 14.2 kWh useable of 16.3 kWh (unless some markets have it different). I believe the buffer however is at the lower end of the battery, because the car needs to maintain certain functionality even with a "depleted" battery. And you can actually drive slowly quite a while on electric at 0% battery.

I also saw some thread where someone actually measured it, but can't seem to find it now.

[Lantirn]

Originally Posted by Swie

Actually it's 14.2 kWh useable of 16.3 kWh (unless some markets have it different). I believe the buffer however is at the lower end of the battery, because the car needs to maintain certain functionality even with a "depleted" battery. And you can actually drive slowly quite a while on electric at 0% battery.

I also saw some thread where someone actually measured it, but can't seem to find it now.

True, doing the math, 100% corresponds to 87,1%, but this only considers the upper limit buffer and that the bottom is zero when zero indicated. If we assume that lower and upper limit buffer is equally distributed, at lower buffer zone at 0 indicated is 6,4% and upper is 93,55%, but again this is an assumption at best scenario.

Math for reference: ( 14,2 x 100 ) / 16,3 = 87,1% of useable battery

87,1% - 100% = 12,9% unusable battery but you have to split it equally for upper and lower buffers, so divided by 2 is 6,4% buffers up and down which is 6,4% at lower and 93,55% at higher limits. That however means that to reach the actual 80% you can then push the charging more, close to 85%.

What looks to be the case is for BMW to have only the lower buffer zone to keep xdrive and horsepower. So the 0 indicated could be 12,9%. Then the 80% charging recommendation makes sense according to manual.

[Lantirn]

Originally Posted by Fish Fingers

In answer to your original question OP.
This was the most referenced post on the other (EV) forum about charging cycles from someone with practical experience at the sharp end of battery technology (tech heavy, but good summary at the end) ...........

I work on satellites that use Li-Ion batteries.

In orbit, we can see tens of cycles a day going in-and-out of eclipse, so maintaining battery health is a critical function since we want these to last for many years in-orbit. While there is numerous different cell chemistries that are used by cell manufacturers, I expect most Li-ion cells to behave similarly from a life standpoint.

While I can't share the actual test report since it's proprietary to the cell vendor, I can share some findings from some of their life testing going through 5000 discharge cycles under various conditions (charge/discharge rate, temperature, depth of discharge):

- Heavy discharge / charge cycles ((C)apicity/2 rates, which would only be ~58 Amps for us - 93kWh battery/800V = ~116Ahr) from 100% to 0% and back caused the biggest degradation - the batteries only lasted <1000 cycles before falling below 80%. While we physically can't discharge at C/2 for more than a few seconds, some of us are likely charging at rates greater than C/5 (23A) regularly.

- Heavy discharge / charge cycles (C/2) from 100% to 60% resulted in a ~10% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 60% resulted in only a ~8-9% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 80% resulted in only a ~5% degradation after 2500 cycles.

- Mild discharge / charge cycles (C/5) from 100% to 90% resulted in only a 2% degradation after 5000 cycles (yes, double the cycles than the other tests performed, with less degradation).

For the space rated batteries, temperature doesn't look to play a big role on degradation, but does impact how fast we can charge/discharge the batteries, so we tend to keep them cold when not in use (0 degC when battery is fully charged), and 20 degC when charging/discharging (we pre-heat before the eclipse, then the draw on the battery tends to be able to keep it at that temp). During long periods of no battery usage (out of eclipse season), we tend to drop the batteries down <80% capacity for storage.

So, what does that all mean? How frequently you charge actually has little effect on battery life - it's really how much battery you 'use'. You basically get the same degradation for the same amount of battery used - 2500 cycles at 20% versus 5000 cycles at 10% end up causing a 4-5% degradation of the total battery capacity (so equal energy used in those 2 cases). And 2500 cycles at the 40% DoD caused 8-10% degradation of the total battery - also in-line. Thus, the biggest limitation on Li-Ion batteries is big discharges (>80%), and heavy charge/discharge cycles (C/2). I know I've seen other test reports that show data for C and 2C discharge rates as well, but I'm not finding them at the moment.

I believe this is all consistent with what EV owners have seen - you don't want to use the fast chargers everywhere, and avoid deep discharges on the battery (<20%). You can potentially extend the life a little bit by charging at even slower rates - I actually backed my home charger off to 20A because I have no savings having it take 8 hours versus 4 hours over night (and I was occasionally getting overtemp warnings on the charging unit on the hot summer days).

Very interesting thread found. Good data here

Although nothing is written (maybe not tested) for high percentage charging to 100% or 80%. All the satellites were charged to 100% in all the tests.

Anyway conclusions can be drawn here:

1. Charge with flexible charger to maintain battery health, avoid fast charges
2. It doesnt matter how many times you charge, but how low the state of charge on the battery is when plugged: So its better to charge when battery is not low to reduce degradation and this is answered my initial question on this thread. You can charge when 40% or 50% or 60% and will not do any harm, its actually better than waiting for battery to go low and then recharge. For PHEVs this is super convenient for days that you go in and out again and again
3. Maybe charging to 100% is not bad for lithium ion batteries, will have to double check that with other sources but, I will stick to OEM manual opting for 80%. Maybe BMW assumes that the owner will deplete full the battery so in that way they will minimize full battery discharges (its going to be 80% to 0% and not 100% to 0%). So in order to avoid telling the customer to charge when 20% which is somewhat difficult and impractical, they tell him to charge to 80% for simplicity. But again this is an assumption.
   again
4. Still according to the satellite tests, big discharges were the limitation so try to charge when above 20% and keep it light on the acceleration pedal

[Fish Fingers]

Originally Posted by Lantirn

Very interesting thread found. Good data here

Although nothing is written (maybe not tested) for high percentage charging to 100% or 80%. All the satellites were charged to 100% in all the tests.

Anyway conclusions can be drawn here:

1. Charge with flexible charger to maintain battery health, avoid fast charges
2. It doesnt matter how many times you charge, but how low the state of charge on the battery is when plugged: So its better to charge when battery is not low to reduce degradation and this is answered my initial question on this thread. You can charge when 40% or 50% or 60% and will not do any harm, its actually better than waiting for battery to go low and then recharge. For PHEVs this is super convenient for days that you go in and out again and again
3. Maybe charging to 100% is not bad for lithium ion batteries, will have to double check that with other sources but, I will stick to OEM manual opting for 80%. Maybe BMW assumes that the owner will deplete full the battery so in that way they will minimize full battery discharges (its going to be 80% to 0% and not 100% to 0%). So in order to avoid telling the customer to charge when 20% which is somewhat difficult and impractical, they tell him to charge to 80% for simplicity. But again this is an assumption.
   again
4. Still according to the satellite tests, big discharges were the limitation so try to charge when above 20% and keep it light on the acceleration pedal

I think your conclusions are spot on.

The satellite battery guy (@squiden) posted on a number of threads on the Taycan Forum and became a trusted source for battery info on there.

The above post was often referenced as being from someone who actually knew what he was talking about.....
Usually when dealers were talking nonsense.

Also worth noting that on the PHEV X1 all charging will be slow (good) as it's max 7.4 kw/h.
Some people are solely charging Taycans on ultrarapid DC chargers (up to 270 kw/h) and batteries still seem OK after many 000s miles.