Mind-you, whilst it can damage a lithium battery to ‘flatten’ it below its minimum voltage, the one in an EV is virtually impossible to get to that point as the vehicle’s battery management system will:Ī/ give you ample warning of a low battery, andī/ eventually shut the car down before the battery is truly ‘flat’. Is considered ‘kinder’ to the battery to not regularly go to a really low level of charge.(‘Charge early, charge often’ is also the mantra for long distance EV driving in these days of restricted charger numbers and sites in areas you are not familiar with). Gives a reserve should you get detoured near the end of your trip or a charger is down.(For long trips, 20 minute stops are a must every 2 to 3 hours anyway and even an 80% charged battery will go for well longer than that).Īs mentioned earlier, this is similar to the recommendation for ICE vehicles.

Get moving and, if you need, do one extra stop during the day for 20 minutes or less to get that 20% when the battery is at 40 or 50% and the charging speed is much faster.

This means that if you don’t need that last 20%, don’t waste your time (and potentially delay others waiting for that charger) by staying there. (LFP chemistry batteries start slowing at slightly higher percentages, but the effect is much the same: DC charging slows as you near the top of the charge). The physics of battery charging is that the time for an EV battery to charge from 0% to 80% is very roughly the same as it takes to go from 80% to 100%. The other reason for only charging to 80% is when you’re at a DC fast-charger. So yes, the top 20% of the battery is available for use when needed, it is not ‘lost’. (For instance, when leaving home for a long trip). The corollary to the above is that you will not ‘irreparably’ damage the battery by occasionally charging to 100% when needed. To give an example, my 13-year-old iMiEV is still on its original battery with a reliable 70km of its original 110-ish km range left. Many are still going with those original batteries, albeit with reduced range. It is also worth pointing out that the early EVs with smaller batteries were almost always charged to 100%, and their batteries did not ‘die’ early as a result. Even charging my Kona electric to 80% for daily driving, I still only need to charge once every two to three weeks. For today’s EV battery sizes, it is also completely unnecessary to charge to 100% on a regular basis. (More on the other main lithium battery chemistry type, LFP, later).įor longevity of EV batteries, it is considered best not to stress them unnecessarily by charging to 100% every time you plug-in. So what is the significance of the 80 per cent charging limit?Ĩ0% is the recommendation for normal day-to-day charging of non-LFP EV batteries, which are still found in most EVs. (This particularly applies to 98 octane petrol, but diesel winter/summer formulations can also cause issues).

Never fill the tank to full if you don’t use the car much to avoid to ending up with months old ‘stale’ fuel.

Don’t go below 1/4 in a fuel tank to avoid running out/sucking up dirt or water from the bottom of the tank and.

So where has this nonsense come from? Like all good urban myths: it is based loosely on a couple of pieces of information that have been taken out of context, and are borne out of “rules” that might equally apply for an internal combustion engine (ICE) vehicle.įor instance, we have long been told when driving petrol or diesel vehicles that: This myth says that batteries should never be charged beyond 80% or discharged below 20% lest ‘irreversible damage’ occur.Īnother slightly different version of this “rule” suggests that if EV batteries can’t be taken safely above or below these limits, then they are really only 60% of their stated size/driving range. The ‘new’ one I am referring to is what I will call here the 80/20 ‘rule’. Or, as I will show here: be recycled in subtly different forms. Even as I wrote it, I knew it wouldn’t be the end of EV urban myths: I might have covered ten of the ‘best’ and put them to bed, but I was sure more would come along to replace them. Some time ago I wrote my list of ‘ Top Ten EV Urban Myths That Deserve To Die’.

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