EV charging advice V0.2 – do we need to go to 100 per cent?

Hi Bryce,

Thank-you for your factsheet on the MG4. (Available at aeva.au/fact-sheets). I have recently bought the MG4 Essence 64. The MG manual that came with the car is not that helpful.

I know I have an NMC lithium-ion battery. But there is conflicting information on the web about the optimum charging profile to ensure the longevity of the battery. At this juncture, I feel the majority of punters opt for a discharge to 20%, then charge to 80% when not about to embark touring.

Do you have an opinion on that?

And then, what do you think about regular topping up to 80% from 50%, 60% or even 70%? Is that wasting cycles?

And finally, the manual mentions needing an equalisation charge regularly between all the cells. But doesn’t say if that only commences once the battery approaches 100%. And the heads-up display in the car doesn’t indicate anything in this regard. Do you have knowledge of cars needing equalisation charge?

Thanks for any response you may provide.

Regards

Tina

Hi Tina – and welcome to the EV grin. (By which I mean the irremovable grin that grows as you instantly accelerate to noiseless, fumeless and low emissions travel). Sounds like that grin might be getting a bit dented by the less-than-helpful MG manual though. 

As an aside, it seems to be a growing trend to provide little or no useful information with new cars. (Including my pet hate: some now come with no owner’s manual at all, instead relying on badly laid-out electronic versions with practically non-existent search functions AND require you to be sitting in the car to access/swear at them …)

In relation to your queries, NMC chemistry batteries are less worried about not being charged to 100% from time to time. On the other hand, LFP ones do need to be taken to 100% every few charges. If LFP isn’t taken to 100% relatively regularly, it ‘forgets’ what the fully charged battery capacity is through some cells getting out of balance.

Even for NMC, their cells do like an occasional ‘top balance’ to equalise the voltages at the fully charged level from time to time. 

In your case, I would suggest charging to 100% every month or so and/or whenever you have a longer day’s travel the next day. 

Personally, I don’t bother too much about it and only charge to 100% on the random times when I remember I haven’t done so for a while. (BEV battery management systems have progressed a long way since I was doing EV conversions and are now far more forgiving of non-technical users).

I did also write an extensive article on the myth that EV batteries only operate between 20 and 80% some time ago – you can still find it here by the way.

In general, it’s just a new regime to get used to (as discussed in another article I wrote early last year) – in the same way we have had instilled into us from birth regarding petrol or diesel cars. As per the second article link, be it petrol, diesel or EV: you don’t fill it to the top unless you’re about to do a lot of kms. 

For a petrol car left sitting with a full tank, the petrol can go off giving poor performance and using more fuel. For an EV, the battery can age slightly faster as it is being ‘stressed’ when left at its highest level for longer. (Not that there is not a huge amount of EV driving evidence for that – but theoretically that is the case).  

Ditto BTW for going below 10-15% – in a petrol car we’re used to not doing so because you can suck up dirt and water from the bottom of the tank, for an EV you are stressing the battery if you leave it at that for weeks to months. (Plus risk a flat 12V battery when you do try to get going because it quietly shut down to protect itself after weeks of maintaining the systems!)

All-up, for day-to-day use charge an NMC battery when somewhere under half up to 80% or 90%. It’s no real issue to charge from 70% to 80% a lot – NMC batteries have enough cycles in them to last the life of most cars.

(LFP do have more again, but all that means is they will far outlast the car!). On the other hand, charging often does add wear and tear to the socket and plug, which may/may not become an issue in the long run. 

Charging to 100% before a long trip the next day is also fine, as is occasionally running down to 5% (or even less) to make it to a destination – provided you plug in when you arrive and take it up to 20%-ish. 

Hope that helps?

Cheers

Bryce