Should I charge to 100%?

Generally, I think we shouldn't keep it for a long time at 100% or at very low charges.

The Zoe ZE50 uses LG Chem NCM 712 E78 cells. The VW id3 also uses E78 cells. VW recommend only charging to 80%. The Zoe battery warranty runs for 8 years or 100k miles but only applies if the battery falls below 70% state of health which is a pretty poor battery. If you want to maximise battery life you should avoid high ambient temperatures as far as possible, minimise fast charging and try to keep the battery as close to 50% charged for as much of its life as possible. If you regularly fast charge and keep it fully topped up it will still last a long time (and not trigger the Renault warranty) but not as long as if you treat it gently, as above. This has been an established and well understood characteristic of NCM Lithium cells for many years. One of the reasons 80% is often referenced is that fast chargers usually slow the charging rate considerably at this point which is a different issue - in normal home charging 80% is not a magic threshold, 70% is better, 65% better still etc but 80% is a good compromise. If you need 100% for regular long journeys then fine but your battery state of health should be expected to degrade slightly more quickly.

I agree that an occasional full charge is a good and necessary thing to do. From what I have read, charging to 100% and particularly leaving the battery at 100% for extended periods will not do any "harm" as such but it is not the optimum way to store a battery for the minimisation of degradation. Panasonic research on early 18650 showed that high charge was actually worse for a battery than allowing the battery to go to a very low state of charge. The BMS will not allow any individual cell to be fully depleted or for that matter, to be over-charged.

I believe that you should occasionally (perhaps once a month, depending upon usage) charge to 100%. The reason for this is that it allows the cells to be balanced and do not believe that it will cause any harm, as the BMS will not allow an overcharge. As has already been stated, it is important to not leave it sitting at 100% for any appreciable amount of time. I think that the main thing to avoid is allowing the SOC to go too low. Each cell is slightly different. If you are running at 10% SOC, you will have a few cells that are actually at 0%. The other cells will then be attempting to charge them. Both sitting at 0% and having other cells attempting to charge them are both very bad situations for the dead cells, which should be avoided. So, to recap, I am happy to charge to 100% as required and use the car immediately but I will avoid going below 20% unless absolutely necessary. One further point. When you charge to 100%, I find that the power loss is around 18% (charger output vs kw received), which is quite a high loss. My normal power loss charging to 90% is around 5%. This is using a 22kw 3-phase with an appropriate cable.

Unfortunately I'm not a technical expert either, but have destroyed and needed to replace lots of lithium ion batteries in the past as I race them in model cars and poor chargers are the main culprit. Below is just my experience with lithium ion batteries and I should also say that the maximum charge voltage referred to below may also change slightly  as development in battery technology occurs.

One fundamental difference between nickel metal and lithium ion batteries is the way they can be charged, nickel metal is not as voltage critical, you can keep charging these and increasing the voltage until you see a peak in cell voltage which is a sign that the cell is fully charged.

You cannot charge a Li Ion cell in this way if you do it will just swell and may eventually burst into flames, these cells have a maximum voltage per cell which I is around 4.2v, you cannot exceed this voltage, if you do the cell will rapidly degrade and swell. The charge rate will also effect the charge voltage because the higher the charge rate the higher the voltage will be needed to force current into the cell. This is why I have heard them say these cells charge much slower above 80% (in the case of my model cars its 90%) this is because once the charge voltage reaches the cell maximum voltage the charge current reduces to ensure the charge voltage never exceedes the cell maximum voltage. (Hope that makes sense.)

So, I guess a battery which has been charged to 100% is probably sitting around it maximum voltage (depending on what the battery management system -BMS- will allow), this is where the degregation really starts to take off, in the case of the battery I am assuming this is not an ideal place to be, changes in outside temperature for example will effect the efficiency of the cell and may cause its voltage to increase, potentially above the maximum threshold and exaggerate the degregation process. I guess this is not such a concern when a battery which is charged to 100% and then immediately used which will drop the voltage below the threshold, but a battery which has been charged to 100% and then left standing for days is not ideal.

In my case, I have just bought may Zoe Z50 and had my charger installed, the charger is set to a maximum car charge rate of 75% and I typically only use it for local runs so the 7kw home charger is more than suitable and 75% charge gives me plenty of range.

I have not mentioned this but these batteries also have a minumum cell voltage which is around 3v per cell, once again below this degregation occurs. Hope this helps Richy.

5

I think it's all nonsense, just charge it to 100% and don't worry. Modern batteries have come a long way. By the time it has any effect (if it actually does) , you will probably be buying a new car anyway.

Increased aging does not come from charging to 100% but from leaving the battery at 100% for extended periods. Ideally keep your battery as near 50% as you can afford to while still being able to use the car as you wish. If your journeys are short and predictable this won't be difficult.

Remember the battery is a consumable item and will degrade over time/use. the 20-80 charge opinion should extend the life of the battery. However it will degrade anyway, slow charging is probably better for the battery as high power charging increases the battery temperature rapidly. There are many youtube channels who breakdown the 20/80 charging phillisophy and can explain it better than me!

I am certainly not a “ technical expert” and have only had a Zoe since December 2022 but I would think that logically, if the battery is able to be charged up to its 100% capacity, then doing this would not damage the battery. If this indeed was not the case then I would suggest that the manufacturing process would be such as to have designed a product that was not “ fit for purpose”. It would almost be like having a petrol car that in some way was “damaged” by fully filling up its petrol tank.

I would suggest, although not based on any particular knowledge, that the only possible relevant factors MIGHT be the frequency of charging and the speed of charging. I can see some logic in the battery having some sort of optimum number of charges and possibly losing some of its total capacity once this optimum number is exceeded….I would imagine this optimum number would be very high.

I would also imagine that more the rapid the charging speed the more the “wear” on the battery. I view the 7 KWh charger as the norm……gentle charging / long time. Although I have never used a 22KWh charger I would regard this as a convenient option but would imagine it would have some , hopefully minimal , detrimental effect on the battery life / long term capacity.

The above is of course only the views of a very non expert. It would be nice to get a technical experts view.