Battery expert, Dr Euan McTurk, explains how to keep your EV’s battery in great shape during irregular use

A major effect of the Coronavirus lockdown has been significantly reduced car use. Being compelled to stay at home and not undertake unnecessary journeys has had numerous benefits – better air quality and minimal expenditure on fuel – but what about your EV's battery?

When your daily routine is thrown into disarray, like it probably has been thanks to the Coronavirus outbreak, we kind-of have to re-learn our habits. From commuting, to childcare, to simply going down the shops; everything's different at the moment. Of course, this does mean we're driving a lot less – which for many is a good thing. However, most people will know that leaving a petrol or diesel car undriven for a long time can be bad for the greasy bits. But what about EVs?

Dr Euan McTurk – Electrochemist at battery boffins Dukosi, YouTuber and all-round EV expert – offers some handy pointers of what to do, and what not to do to keep your EV's battery in great shape! Over to you Dr Euan...

The headline here is to keep the State of Charge (SOC) between 50 per cent and 80 per cent charged. 50 per cent is high enough to limit the chances of the battery being left for so long that it is overdischarged by the vehicle's electronics, whilst 80 per cent is low enough to prevent the electrolyte degradation. Let me explain in more detail:

  • Why you should avoid fully charging the battery: When the battery is at, or very close to, 100 per cent State of Charge (SOC), the electrolyte gradually degrades against the cathode, or positive terminal of the battery. This reduces the capacity and performance of the battery pack. Charging to 100 per cent is fine if you're going to use the car again in a few hours' time, but will degrade the battery if it is kept fully charged for several weeks or months.

  • Why you should avoid leaving the battery at below 20 per cent: Whilst a typical lithium-ion cell has a self-discharge rate of two per cent per month maximum, an EV battery will discharge much faster due to the parasitic drain of the vehicle's electronics (the natural discharge from the car simply 'being'). Batteries kept below 20 per cent and left unchecked for several weeks run the risk of being drained by the vehicle's own systems.

Some of my top tips:

  • If your EV has the ability to adjust the charging SOC limit, set it to between 50 per cent and 80 per cent to make your life easier.

  • Keep an eye on the battery's SOC at least once a week via the vehicle's app if it has one, and give it a top-up charge if needs be.

  • Don't forget the 12V auxiliary battery, which powers things like lights, windscreen wipers and infotainment. This gets topped up when the traction battery is engaged, for example when driving or charging. Note: leaving the vehicle plugged in for weeks can interfere with the regular charging of the 12V battery on some models, so unplug when charging has finished and plug in again when needs be, just to be sure. It's a good idea to top up the auxiliary battery about once a week.

  • If the traction battery doesn't need to be recharged, but the 12V auxiliary battery needs its weekly top-up, run the auto-demist function (if your EV has it!) for a few minutes. This not only tops up the 12V battery from the traction battery (you could even say that the car is "self-charging", eh Toyota?), but helps to remove moisture from the cabin. Note: on some models, auto-demist only tops up the 12V battery if the car isn't plugged into the mains.

  • Tesla electronics can be quite thirsty, especially if Sentry Mode is engaged. Expect battery drain to be high compared to other EVs and don't forget to check the SOC every few days.

A final word:

The above advice equally applies to vehicles being parked up for people who go on holiday for several weeks, so it's something to be mindful of for both existing EV owners, and those thinking of buying one. Check out my video below for an easy-to-digest explainer!

If you enjoyed reading Dr Euan's advice and watching his (rather brilliant) video, we can heartily recommend you check out, and subscribe to his YouTube channel – Plug Life Television. It really is a fantastic resource for both education and entertainment. Dr Euan can also be found on Twitter at @106Euan – so give him a follow over there too!

In the meantime as well as keeping yourself safe, if you follow the advice given above you can be sure that when this is all over your EV and its battery will still be in rude health.


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