Nothing is better for an electric car than taking it out for a run virtually every day. That’s how you get the most out of the battery before it starts degrading over time. But if you do have to immobilise your vehicle for several days – or even weeks, there are some precautions you should take. The current call to restrict travel against the backdrop of the pandemic means we should be asking and answering a few questions.
Time degrades lithium-ion batteries
In an electric vehicle, the operational lifespan of a lithium-ion battery may be between 8 and 10 years – and can sometimes extend beyond that.
When the energy capacity falls below the threshold of 75%, battery packs can still be used as stationary storage units coupled, for example, with intermittent renewable sources (wind, solar), rapid charging stations (to avoid connections requiring costly subscriptions and building work), or the grid at home or at work (as a back-up or to save money on the electricity bill).
Different causes may lead to further deterioration in traction batteries, some of which can be traced back to vehicles being immobilised over a period of time.
Storing fully discharged
Between 1995 and roughly 2005, people were advised to store the batteries of their EVs fully discharged. But that was back in the days of nickel-cadmium technology and indeed, as long as no energy-consuming devices were active, this was the best action to take for a longer battery life.
However, it is absolutely forbidden to discharge lithium batteries to any great degree, with the minimum value being 2.5V and 3.3V respectively for lithium-ion and lithium-ion polymer batteries. Beyond this point, irreversible damage can be caused due to undesirable chemical reactions.
In extreme cases, such deterioration is suspected of causing packs to catch fire, either during recharging or after being immobilised for a long time. This phenomenon is becoming increasingly rare and is on the verge of disappearing altogether as technological advances come in. However, even today cells may die due to long storage when fully, or almost fully, discharged.
Two points should be borne in mind on this subject: lithium-ion cells self-discharge automatically by about 3% per month (the precise value depends on the chemical make-up); devices placed in stand-by mode draw energy from the traction battery slowly but surely and directly or indirectly.
Storing fully charged
Storing a lithium-ion pack at 100% of its capacity is not recommended either. Even with self-discharging, this will lead to premature ageing of the cells.
For example, this Nissan Leaf from 2011 showcased for 5 years at a dealer’s garage with a fully charged battery. By 2019, it only had a range of 45 kilometres. The 70% loss of its capacity is also due to other factors, including a constantly high ambient temperature of between 28 and over 35°C.
In any case, owners of electric vehicles that have been stored with a full battery all report a premature loss of range. Mobile devices such as phones or laptops would have been unusable much earlier on.
However, we should bear in mind that even with a battery kept in optimum conditions, an electric car will lose some of its range after 5 years off the road due to its age. Albeit to a lesser degree.
50, 60, 75%?
What is the best energy capacity to aim for when immobilising your EV for several weeks, months or years? The best bracket is between 50 and 75%. This gives enough leeway for monitoring not to be too time-consuming.
But there’s no doubt about it – lithium-ion batteries are best when used on a regular basis. No particular problem arises when you leave your battery within this bracket for a couple of weeks. But if the rest period extends beyond one month, you need to think about providing the pack with some activity by recharging it for a few dozen minutes and taking your vehicle out for a spin from time to time.
Especially as the secondary 12V battery may become flat after a few weeks. This is particularly true for certain EV models, and especially when batteries are coming to the end of their lifecycle. This phenomenon is virtually unnoticeable when you use your vehicle on a regular basis. But after of few weeks of immobilisation at temperatures below zero, lead-acid batteries will age rapidly and visibly.
Tips for discharging your electric vehicle
In the current climate where travel is restricted to the bare necessities, it may not be easy to drive around for the few dozen kilometres required to reduce the charging level.
The ideal solution would be to lend your vehicle to someone who needs it for one or more priority trips. If this can be done safely, of course, with no risk of transmitting or receiving the Covid-19 virus.
Another possibility would be to run one of the more energy-guzzling features such as the heating system – making sure that you leave the windows open. The greater the battery’s capacity, coupled with an efficient device (heat pump), the more time you need to spend doing this.
What works for private individuals is all the more true for businesses with a fleet of electric vehicles.
With the exception of models fitted with Bolloré LMP batteries on Bluecars and their derivatives (Bluesummer and Citroën e-Méhari), it is not recommended to leave your EVs connected for several weeks or months without taking them out for a drive.
The exception is vehicles equipped with devices which automatically stop charging when the capacity reaches over 80%. This precaution is also valid for non-professional EV drivers. This type of automatic feature is helpful in times like the present crisis – as long as you thought of it beforehand.
With a bi-directional charger (a lucky few are already equipped), it will soon be possible, particularly for professionals, to draw on the battery energy of electric vehicles to feed into the national grid if necessary with V2G (Vehicle to Grid), V2H (Vehicle to Home) and V2B (Vehicle to Building).
Once this is up and running, all our advice will become null and void for all equipment connected via this type of system – and so much the better! Packs will undergo a salutary exercise on a regular basis with charging, discharging and rest phases several times a day.
To summarise: if the vehicle is immobilised for a couple of weeks, you are advised to keep the battery of your EV charged at a rate of 50 to 75%.
If the situation extends beyond one month, you need to give the battery some activity with operations that alternate charging and discharging, while remaining within the 50% to 75% bracket.
This article is a translation.
Original article from Automobile-Propre.