Last year, I wrote a post quantifying the cost of home EV charging across the US. Given the low prices of home electricity, it’s no surprise that EV owners choose to slowly top up their batteries each night at home, and avoid more expensive public chargers.
However, it’s a safe bet that nearly all EV owners will eventually find themselves in need of a public fast-charger! And when that happens, they’ll almost certainly be looking to charge their vehicles as quickly as possible, and get back on the road.
With this in mind, I thought it would be interesting to look at the key determinant of fast-charging times: the “charge curve”, which defines the relationship between charging speed (in kW) and battery level. Very generally, the “emptier” the battery, the more quickly it will charge - and then as the battery “fills up”, it will typically charge more and more slowly.
However, there is a lot of nuance into how these charge curves look, per model and per manufacturer. Furthermore, battery architectures vary quite a lot across vehicles, so certain models may have peak charging speeds two or three times higher than other models at across the charge curve.
I could blab on all day about these differences (like how it’s neat that the mainstream Hyundai Ioniq 5 and Kia EV6 have the same 800v architecture as the Audi e-Tron GT and Porsche Taycan, which allows them to have some of the fastest peak charging speeds on record) - but sometimes it’s best to let the data do the talking!
Visualizing Charge Curves
Take a peek at the graphic below, which visualizes the charge curves of popular EVs, grouped by their general vehicle “class”, to help clean things up.
A few observations which stuck out:
- The flatness of the EV6/Ioniq 5 charge curve through the first half of the battery is remarkable - meaning “quick” fill-ups from 10-50% battery will absolutely fly by. Quick math (40% of an ~80 kW battery = 32 kW, at 225 kWh) shows that this level of charge will take just 8.4 minutes!
- More affordable vehicles pretty much uniformly have battery architectures which charge more slowly - the Niro and Kona being great examples of EVs which seem to trade off peak charging performance for affordability
- Some models clearly prioritize peak charge speeds, like the e-Tron GT and i4, at the cost of charge speeds higher in the battery register, which drop off more sharply
- Others have clearly sought to have lower peak charging speeds, but to maintain higher rates throughout the battery register. The e-Tron is a great example of this, with charging speeds of 150 kWh across pretty much the entire battery range!
- Looking across all the faceted plots, a general rule of thumb around charge speeds seems to emerge: users should expect maximum charge speeds when battery levels are at a minimum, and should generally expect charging speeds to be twice as fast at 25% battery than at 75% battery