The number on the side of a charging cabinet is a ceiling, not a promise. What you actually get depends on your battery’s state of charge, its temperature, and how many other cars are sharing the same cabinet. Understanding the charge curve is the difference between a 20 minute stop and a 50 minute one.
- Charging speed falls as the battery fills. The 10 to 80 per cent window is where nearly all the useful speed lives.
- A cold pack charges slowly. Preconditioning on the way to the charger is the single biggest thing you control.
- Many sites share power between paired stalls, so a neighbouring car can halve your rate.
- Plan stops as short top-ups rather than one long charge to 100 per cent.
What the charge curve is
Plot power against state of charge during a DC fast charge and you get a curve that rises quickly, holds a peak for a short window, then tapers steadily towards the top. Peak power is usually available somewhere between roughly 10 and 40 per cent, and the taper past 80 per cent is steep on almost every car sold today.
The taper is not a manufacturer being cautious for its own sake. As lithium ions pack into the anode, the cell’s internal resistance rises and the risk of lithium plating increases. The battery management system reduces current to keep the cell within a safe voltage and temperature window. That is protection you want.
Why the last 20 per cent takes so long
As a rule of thumb, charging from 80 to 100 per cent often takes about as long as 10 to 80. On a road trip that time is almost always better spent driving to the next charger. The exception is when the next reliable charger is far enough away that you need the buffer, or when you are charging overnight at a slow AC point where the taper barely matters.
| Charging window | Typical behaviour | Best use |
|---|---|---|
| 10 to 40 per cent | Peak power, fastest kilometres per minute | Road trip top-ups |
| 40 to 80 per cent | Gradual taper | Finish the stop here |
| 80 to 100 per cent | Slow, sometimes very slow | Overnight AC, or before a long remote leg |
Temperature matters more than most people expect
A cold battery physically cannot accept high current. Below roughly 10 degrees Celsius, a pack that has not been warmed may accept only a fraction of its rated power until it heats up, and some of the energy going in is spent warming the pack rather than filling it.
Most modern EVs can precondition: if you set a fast charger as your navigation destination, the car warms the pack on the way so it arrives ready. On cars that offer it, this is the single most effective habit you can build.
Navigate to the charger in the car’s own navigation, not just your phone. On many EVs that is what triggers battery preconditioning, and it can cut a winter stop dramatically.
Power sharing, and why your neighbour slows you down
Many charging sites pair two stalls to one power cabinet. Plug in alone and you may get the full rated output. Plug in next to an occupied stall and the cabinet may split its output between you. This is normal, it is rarely signposted, and it is a good reason to prefer sites with more independent stalls.
Chemistry and architecture change the shape
LFP packs tend to hold a flatter curve for longer but are more sensitive to cold. High voltage architectures, commonly marketed as 800 volt systems, can sustain higher currents with less heat, which is why they often post the shortest 10 to 80 times. Neither guarantees a fast session on a weak charger.
How to plan a stop
Arrive with a low-ish state of charge, ideally under 30 per cent, at a site with several stalls, with the pack preconditioned, and leave at around 80 per cent. Two short stops usually beat one long one. If a session starts unusually slowly, unplug and try a different stall before assuming the car is at fault.
Frequently asked questions
Why does my car charge slower than the charger is rated for?
Because rated power is a ceiling, not a delivery promise. Your actual rate depends on state of charge, battery temperature and whether another car is sharing the same power cabinet. A high state of charge alone can cut the rate by more than half.
Should I charge to 100 per cent on a road trip?
Usually not. Going from 80 to 100 per cent often takes about as long as 10 to 80, so you gain relatively little range for a lot of time. Charge to 100 only when the next reliable charger is far enough away that you need the buffer.
Does fast charging damage the battery?
Occasional DC fast charging has a small measurable effect over the life of the pack, and the battery management system actively protects the cells. Charging almost exclusively on DC, especially with a hot or very cold pack, has more impact than the same energy taken slowly at home.
