The EV Charging Curve Explained for Drivers in Malaysia

When you fast charge an electric vehicle (battery electric vehicle, or BEV), the speed is not constant. It is quick when the battery is low and slows down as the battery fills, especially in the last stretch toward full. That rising-then-tapering pattern is the charging curve, and it is the single most important thing to understand about DC fast charging. This guide explains why the curve happens, why 20 to 80% is the smart fast-charge band, and how the curve is the reason the calculator on this site shows two different charging times for the same charge in Malaysia.

By mht-dev, Frontend Engineer & Creator

A frontend engineer who bought a first electric car in March 2026 and built EV Charge Calculator while working out the real cost of charging it, writing every guide from an everyday new EV owner's perspective.

Why charging speed is not constant

On a DC fast charger, an EV pulls its highest power when the battery is fairly empty. It holds near that peak while the battery is low, then the car's battery management system gradually reduces the power as the battery fills. The reason is the way lithium-ion cells charge. Early on the charger pushes a steady high current into the pack (the constant-current phase). As the cells approach full, their voltage rises and the system switches to holding the voltage steady while the current falls away (the constant-voltage phase). Pushing hard current into an almost-full cell would raise voltage and heat to levels that stress and age the battery, so the taper is a deliberate protection, not a fault.

The taper is gradual, not a cliff at one fixed point. For many cars the rate begins to ease off somewhere between 60 and 80%, is down to roughly half the peak by about 80%, around a quarter of the peak by about 90%, and crawls through the final few percent to 100%. The exact shape varies a lot by model, by battery temperature, and by the charger, so treat these as a typical pattern rather than precise figures for any one car. The takeaway is consistent across every EV: the first part of a fast charge is the fast part, and the closer you get to full, the slower each extra percent becomes.

Why 20 to 80% is the DC sweet spot, and 80 to 100% is slow

Because power is highest in the low-to-middle part of the curve, you add the most range per minute in the 20 to 80% band. That is why it is the everyday fast-charge target: you get the bulk of your range back in the shortest time. Above 80% the taper bites hard, and this leads to the headline fact about fast charging: going from 80 to 100% can take about as long as going from 10 to 80%, even though it adds far less range. The last fifth of the battery is simply the slowest fifth to fill on DC.

There are two practical lessons. On a public DC charger, stop near 80% on a normal stop: you have already collected most of your range, and you free the charger for the next driver instead of crawling to 100%. When you genuinely need a full battery for a long drive, do that part on a home AC charger overnight, where the slow speed near full does not matter because you are asleep anyway. For the other things that cap charging speed, such as charger power, the car's own limit, a shared charger, and battery temperature, see the companion guide on what affects EV charging speed; this guide stays focused on the curve itself.

How this shows up in the calculator and on the car pages

The charging cost calculator on this site shows two charge-time rows, and the curve is the reason there are two. The first, Charging time, is the simple theoretical figure: the energy you need divided by the charging power you set, as if the car drew that power the whole time. The second, the Realistic estimate, applies the taper, so it reflects that the last part of a fast charge is slower than the flat calculation suggests. Energy and cost are the same in both views, because energy and cost depend only on how many kWh you add, not on how fast you add them. Only time changes, because time is the one quantity the curve affects.

The two rows match exactly when you charge on AC, and they diverge on DC at a high target percentage. The reason is the limiting factor. On a home or public AC charger (commonly around 7 to 22 kW), the car's small onboard charger, not the battery, is the bottleneck, so the power stays flat across the whole charge and there is no taper to apply: the realistic estimate equals the simple figure. On a DC fast charger the battery itself becomes the limit at high state of charge, so the taper kicks in and the realistic estimate grows longer than the flat figure, most of all when your target is above 80%. If you only ever fast charge from a low battery up to 80%, the two times stay close; aim for 100% on DC and the gap opens up. To see this for yourself, open the calculator, pick a car, and compare the two rows as you raise the target percentage.

The per-vehicle pages use the same curve in their charge-time tables, so the whole site tells one consistent story. For popular models we anchor the estimate to a measured 10 to 80% fast-charge time, which makes those figures closely match real life. For the long tail of models without a measured time, we apply the same generic curve to the car's peak DC power, clearly as an estimate. Either way the figure is an estimate that varies by model, temperature, charging power, and the exact percentage range, so use it to compare cars and plan stops, not as a stopwatch promise. For how AC and DC differ in the first place, see the AC versus DC charging guide; for the 20 to 80% habit and battery longevity, see the battery care guide.

Frequently asked questions

Why does my EV charge slower as it fills up?

It is the constant-current to constant-voltage transition in lithium-ion charging. While the battery is low, the charger can push a high steady current, so charging is fast. As the cells approach full, their voltage rises and the system holds the voltage steady while letting the current fall, to avoid the heat and stress of forcing power into an almost-full cell. That is the taper, and it is built into every EV to protect the battery. It is why the start of a fast charge is quick and the end is slow.

Why does the calculator show two charging times?

The first time, Charging time, is the simple theoretical figure: the energy needed divided by the charging power, as if the car charged at that power the whole way. The second, the Realistic estimate, applies the charging curve so it reflects the slowdown near full. They match on AC charging, where the onboard charger is the limit and power stays flat, and they diverge on DC charging at a high target percentage, where the battery itself limits the rate and the taper makes the real time longer. Energy and cost are identical in both, because only time is affected by the curve.

Why is 20% to 80% the recommended fast charge?

It is the part of the curve where power is highest, so you add the most range per minute. Charging much above 80% on DC runs into the steep taper, where each extra percent takes disproportionately long, so going to 100% can take about as long as the whole 10 to 80% stretch for a fraction of the range. Stopping near 80% on a fast charger is therefore quicker overall, frees the charger for others, and is gentler on the battery. Charge past 80% mainly when you really need the extra range for a long trip, and do that on a home AC charger overnight where the slow speed near full does not cost you any waiting time.