to be honest, if battery becomes an issue - don’t really care as will only use it for 3 years and then get rid of the car.
Sure, lots of info on the web, just search for ‘EV batter balancing’. Concept is pretty standard for all multicell batteries. I found about this for Tesla’s, and showed results, also tried on my wife’s Renault, again seen results and we have continued to do this from time to time over the last 3 years.
Here is one from a member discussing this with a Porsche engineer.
Typically charge to 80-85% on a daily basis, no harm in charging 90-100% once in a while on as needed basis, but never let a car sit on a 100% charge overnight or for several hours. That can lead to accelerated battery degradation.
I’m at 36,000 miles in a smidgeon under 2 years and my usage profile has me charging to 99/100% a lot as this works best for my current needs. Occasionally due to Octopus Intelligent/cancelled work this has left the car in 100% charge state for a reasonable period of time. I’ve not got an ODB reader but I’ve noticed no appreciable loss of range in this time. My sense is that you’re right that Porsche BMS is quietly beavering away in the background looking after things, with the caveat that I’m not an engineer. Also, most of that charging has been done on Ionity fast DC.I think the “never let a car sit on a 100% charge overnight or for several hours' is poor advice. You can do this without compromising the battery providing the car has a decent BMS. I assume the Taycan does have a decent BMS?
I'm new to this forum (just bought a used Taycan) but have significant experience in Lithium batteries. I haven't read all the data in previous threads on charging but can input from a external perspective. In my day job, I am technical director of a company involved in recycling Lithium EV batteries. This means recovering the important metals as oxides from battery black mass (ie Lithium, Nickel, Manganese and Cobalt) and then reforming them into cathode materials. I do understand the chemistries of these batteries. I also have 5 years experience of fitting a 5 kWh bank of LiFePO4s (Winston Thunderskys) to a boat – which we spend a lot of time living on, which required me to build my own simplistic BMS to stop overcharging or sub zero temperature charging- so have first hand experience of what can and does go wrong when you charge up to 100% with LiFePO4s. Finally I have 3.5 years experience of charging a Tesla M3 with many charges overnight up to 100%.
Firstly around the chemistry. The reason everyone is warned against going over 90% is that the voltage of the cells at that SoC is well into the 'knee' of the voltage curve and so the voltage increases in each cell at a much faster rate than when on the 'plateau' of the curve when charging. What you must avoid is any cell reaching its critical voltage. On my boat LiFePO4s that is 4.2V. My cells reach the knee at 3.5V and my BMS is set to cut charge at a max of 3.6V on any cell. The problem is that when you are at voltages in the knee, battery imbalance is more likely to happen, so you can get cells that could be up over 4.0v with others still down at 3.6V. That is the danger. Once the cells pass the critical voltage then things like dendrites form between the anode and cathode and then shorts and thermal runaway. Stopping the charge at the optimum voltage is key here and I am sure the Taycan is very well designed to do this. Holding then at that high voltage, whilst not recommended for long time (ie days), is unlikely to do much damage in the shorter term ie hours. Not much is likely to happen to the chemistry, unless say a big increase in ambient temperature – but that wont happen overnight.
Charging into the 'knee' with higher power DC charging I would avoid as it is far better to charge slower in this voltage regime.
One thing that is worth noting is the energy held in these batteries. In work, we did a lot of destructive testing for a project aimed at designing transport packaging for Li batteries on aeroplanes (Eu legislation) and found that a small AA size Li battery, when 100% charged, would give quite a serious explosion when pushed to thermal runaway whereas a 30% charged cell was very underwhelming. I would hate to be near a 90kWh car if it caught fire at 100%. LiFePO4 chemistry is much safer than most other Li chemistries, which is why I use it on a boat – that is the last place to want a thermal runaway.
On our boat I do only charge normally to 80% to avoid getting any in-balance in the cells. When installed I did a manual balance and check this circa once a quarter and in 5 years the cells remain in balance. If I took it above 90%, I would expect to see a significant drift to in-balance (experience from other boat users). I do not have a rebalancing system – hence I stay below 80%. In an EV, there will be a balancing system in the BMS but this only works when you get in the voltage knee. When you are on the voltage plateau, you cannot tell the SoC of a cell and a 'laggard' cell at 60% SoC may be one of the highest voltage cells once you get into the knee. You only know which cells to balance once you are up in the 85-90% and above SoC range – so it is important to go up to 100% now and again. Also the SoC will become a nonsense if you dont get up to 85-90% SoC now and again, as SoC is not a measurable value (ie it is calculated via current flows and comparison to 100% full).
Finally below is how my Tesla performed over its near 4 year life, one of the better battery performances compared to its peer group. 70% charging was AC and 30% DC. Of the AC charging, I would estimate 20% of the time I took it to 100% overnight – and drove it the following day. My car was in the top decile of battery performance for the peer group.
I would contend that charging to 100% overnight and driving the following day does little to degrade your battery.
Mr B ......are we related?
Thanks for that data. Interesting.
I think I read somewhere a rather nice analogy that filling the battery is a little like trying to fill a sports stadium to full without allocated seating. The first 80% get seated pretty easily but the last 20% are sort of climbing over one another to get to the remaining seats. I’ve no idea if the analogy is accurate, but I rather like it!
Thankyou for taking the time to write all that.I think the “never let a car sit on a 100% charge overnight or for several hours' is poor advice. You can do this without compromising the battery providing the car has a decent BMS. I assume the Taycan does have a decent BMS?
I'm new to this forum (just bought a used Taycan) but have significant experience in Lithium batteries. I haven't read all the data in previous threads on charging but can input from a external perspective. In my day job, I am technical director of a company involved in recycling Lithium EV batteries. This means recovering the important metals as oxides from battery black mass (ie Lithium, Nickel, Manganese and Cobalt) and then reforming them into cathode materials. I do understand the chemistries of these batteries. I also have 5 years experience of fitting a 5 kWh bank of LiFePO4s (Winston Thunderskys) to a boat – which we spend a lot of time living on, which required me to build my own simplistic BMS to stop overcharging or sub zero temperature charging- so have first hand experience of what can and does go wrong when you charge up to 100% with LiFePO4s. Finally I have 3.5 years experience of charging a Tesla M3 with many charges overnight up to 100%.
Firstly around the chemistry. The reason everyone is warned against going over 90% is that the voltage of the cells at that SoC is well into the 'knee' of the voltage curve and so the voltage increases in each cell at a much faster rate than when on the 'plateau' of the curve when charging. What you must avoid is any cell reaching its critical voltage. On my boat LiFePO4s that is 4.2V. My cells reach the knee at 3.5V and my BMS is set to cut charge at a max of 3.6V on any cell. The problem is that when you are at voltages in the knee, battery imbalance is more likely to happen, so you can get cells that could be up over 4.0v with others still down at 3.6V. That is the danger. Once the cells pass the critical voltage then things like dendrites form between the anode and cathode and then shorts and thermal runaway. Stopping the charge at the optimum voltage is key here and I am sure the Taycan is very well designed to do this. Holding then at that high voltage, whilst not recommended for long time (ie days), is unlikely to do much damage in the shorter term ie hours. Not much is likely to happen to the chemistry, unless say a big increase in ambient temperature – but that wont happen overnight.
Charging into the 'knee' with higher power DC charging I would avoid as it is far better to charge slower in this voltage regime.
One thing that is worth noting is the energy held in these batteries. In work, we did a lot of destructive testing for a project aimed at designing transport packaging for Li batteries on aeroplanes (Eu legislation) and found that a small AA size Li battery, when 100% charged, would give quite a serious explosion when pushed to thermal runaway whereas a 30% charged cell was very underwhelming. I would hate to be near a 90kWh car if it caught fire at 100%. LiFePO4 chemistry is much safer than most other Li chemistries, which is why I use it on a boat – that is the last place to want a thermal runaway.
On our boat I do only charge normally to 80% to avoid getting any in-balance in the cells. When installed I did a manual balance and check this circa once a quarter and in 5 years the cells remain in balance. If I took it above 90%, I would expect to see a significant drift to in-balance (experience from other boat users). I do not have a rebalancing system – hence I stay below 80%. In an EV, there will be a balancing system in the BMS but this only works when you get in the voltage knee. When you are on the voltage plateau, you cannot tell the SoC of a cell and a 'laggard' cell at 60% SoC may be one of the highest voltage cells once you get into the knee. You only know which cells to balance once you are up in the 85-90% and above SoC range – so it is important to go up to 100% now and again. Also the SoC will become a nonsense if you dont get up to 85-90% SoC now and again, as SoC is not a measurable value (ie it is calculated via current flows and comparison to 100% full).
Finally below is how my Tesla performed over its near 4 year life, one of the better battery performances compared to its peer group. 70% charging was AC and 30% DC. Of the AC charging, I would estimate 20% of the time I took it to 100% overnight – and drove it the following day. My car was in the top decile of battery performance for the peer group.
I would contend that charging to 100% overnight and driving the following day does little to degrade your battery.
Yes, the Porsche engineer was extremely knowledgeable and helpful. He was one of only 11 Techs in the US qualified to work on the battery.
