Charging Curve and the 80% Rule: Why Stopping at About 80% Usually Pays Off
📅 Published on 21 October 2026
Information as of 21 October 2026. This article draws on a piece by ADAC (the German automobile club) dated 18 March 2026, a guide from firmenauto.de and a guide from sparneuwagen.de. Figures for individual cars come from the sources named and can differ with other software versions, temperatures or chargers. The worked example uses explicitly assumed values, not measurements.
"Only charge to 80 percent" is a sentence almost every EV driver has heard. It is often understood as a battery-care rule. On a long trip, though, it has a very practical reason: for most cars the charging power drops noticeably from around 80 percent state of charge, and the last few percent cost a disproportionate amount of time. This article explains what a charging curve is, why the peak power in a brochure says little about real charging time, what ADAC found on average power, cold weather and preconditioning, and how to turn that into a charging strategy for your next trip.
What a charging curve is
A charging curve plots charging power against state of charge. The horizontal axis shows how full the battery is (0 to 100 percent), the vertical axis shows how many kilowatts the car is drawing at that moment. According to firmenauto.de, an EV's maximum charging power is "only half the truth": what matters is how long the car can hold a high power level.
firmenauto.de distinguishes two typical shapes. The first is the "peak climber" (Gipfelstürmer): it reaches a high power quickly, and the power falls just as quickly afterwards. The second is the plateau type: power stays roughly constant for a long time and only falls slowly at a high state of charge. According to the guide, both types drop markedly at around 80 percent at the latest; with smaller batteries this can happen earlier. Above 80 percent, power tends toward zero.
For you as a driver this means that two cars with the same peak power on the data sheet can need very different times at the same charger. One holds its peak only briefly, the other stays at a high level for a long stretch after the ramp-up.
Why the power falls
High charging power raises the cell temperature, which can damage the battery. The battery management system therefore regulates the charging process to prevent that, as firmenauto.de describes it. In its piece of 18 March 2026, ADAC adds that the battery management reduces power not only when cells are too hot but also when they are too cold. How the curve looks in detail depends, according to firmenauto.de, on the battery type and the manufacturer's philosophy.
The sources we reviewed give no detailed physical explanation (cell chemistry, voltage levels), and we do not invent one here. For practical purposes it is enough to note what all sources agree on: the highest power is available at a low state of charge and a suitable temperature, and the fuller the battery, the slower it charges.
Peak power is not charging time: the 10 to 80 percent average
ADAC considers the average charging power between 10 and 80 percent state of charge the best basis for comparison and states explicitly that the stability of the curve matters more than peak power. It asks manufacturers to quote charging times uniformly for 10 to 80 percent and to publish the average power in that range, for both summer and winter. It also wants battery heating fitted as standard and the battery temperature shown to the driver.
Behind this is ADAC's test method: the vehicles are preconditioned overnight in a 20 °C hall and then charge at a 300 kW charger from Alpitronic. Where the car supports it, battery preparation is triggered through route planning. For the long-distance rating ADAC counts 90 percent of the full-charge range (10 percent residual energy, since people rarely arrive at a charger completely empty) plus the range added in 20 minutes of charging. In the table of the 18 March 2026 piece, the top group has total ranges with one stop of over 800 kilometres. We deliberately do not reproduce the individual values here because the table totals in the piece do not all recalculate with the stated formula. The message stays the same: if you often drive long distances, ADAC advises a car with a long-distance range of at least 600 kilometres (including a 20-minute charging stop).
Worked example: why 80 percent is often faster than 100
The following example uses assumed values to show the order of magnitude. They are not measurements of any particular car, and charging losses (see our article Charging losses in EVs) are not included.
| Assumption | Value |
|---|---|
| Usable battery capacity (assumed) | 60 kWh |
| Energy 10 → 80 % (70 % of 60 kWh) | 42 kWh |
| Energy 80 → 100 % (20 % of 60 kWh) | 12 kWh |
| Assumed average power 10 → 80 % | 70 kW |
| Assumed average power 80 → 100 % | 30 kW |
| Time 10 → 80 % | 42 kWh ÷ 70 kW = 0.6 h = 36 minutes |
| Time 80 → 100 % | 12 kWh ÷ 30 kW = 0.4 h = 24 minutes |
In this example the first 36 minutes deliver 42 kWh (about 1.2 kWh per minute), while the next 24 minutes deliver only 12 kWh (0.5 kWh per minute). The last 20 percent of capacity therefore takes two thirds as long as the 70 percent before it. Whether this holds for your car depends on its curve, but the order of magnitude is the reason ADAC advises starting at a low state of charge and stopping at around 80 percent, because charging beyond that takes disproportionately long (paraphrased from the ADAC piece).
The calculation only applies if you want to keep driving anyway. If you need the last kilometres to reach your destination and the next charger is far away, a longer stop can make sense. Plan it deliberately, though, rather than always charging full "to be safe".
Cold weather and preconditioning
ADAC's piece gives several figures for cold batteries. The same values were already reported in 2023 in an article on an ADAC test of 50 electric cars (leinetal24.de, 2 March 2023), so they apply to the vehicle versions tested at the time and do not necessarily transfer to current models.
- VW ID.3: according to ADAC it reaches a peak of about 125 kW at 23 °C. At −7 °C charging starts below 50 kW, and the ideal curve of a warm battery is not reached.
- Tesla Model Y in the cold without preheating: the battery is heated for about 18 minutes before charging, and the stop grows from 33 to 56 minutes, roughly 70 percent longer.
- Without preheating overall: the ID.3 needs about 50 percent longer, the Renault Zoe and VW e-Up about 40 percent.
ADAC also points out that some automatic battery heating only starts when a charger is set as the destination in the car's own navigation. If you navigate by smartphone or set no destination, you arrive at the charger with a cold battery. According to ADAC, MG and NIO have offered manual battery heating for some time, and other manufacturers are following. The recommendation to drivers is to precondition the battery in cold weather or allow more charging time. How this works in your model is described in the owner's manual; there is no uniform procedure. For more on the cold season see our article EV charging in winter.
Shared chargers: you split the power
A point often overlooked in the ADAC piece: at chargers whose power is distributed across two charging points, each car gets only about half. A 150 kW or 300 kW charger then delivers no more than roughly half its rated power per vehicle. ADAC therefore advises, where possible, not to charge at a charger that is currently shared with a second car. How many charging points a site has and whether they share power is best checked on site at the charger or in the operator's information.
What manufacturers recommend for the charge limit
The 80 percent rule also shows up in everyday battery care. According to sparneuwagen.de (24 September 2026, last changed 7 October 2026), BMW advises a state of charge between 10 and 80 percent for daily use, and VW recommends an 80 percent charge limit for ID models with an NMC battery in short-distance use. For Tesla, MG and VW models with an LFP battery, the guide instead mentions regularly charging to 100 percent, justified for LFP by cell balancing and range calibration. The guide does not substantiate this reasoning, so we do not adopt it as fact. What is certain: for your battery, what your manufacturer specifies in the owner's manual applies.
The guide further says that occasionally charging to 100 percent is unproblematic if the journey starts soon afterwards; regularly charging full and then leaving the car standing for days, especially in summer heat, is described as unfavourable. There is no memory effect in today's traction batteries, and frequent short top-ups are considered harmless. The guide cites no concrete degradation figures or studies, and so we do not either. If you are interested in battery ageing, see Battery health in a used EV.
Important: everyday charging (at home, overnight, with a limit) and fast charging on the road are two different situations. By the manufacturers' logic, an 80 percent limit at home protects the battery; an 80 percent target at a fast charger mainly saves time.
How to plan charging stops with the charging curve
- Arrive at the charger with a low state of charge. According to ADAC the highest power is available at a low state of charge. For "peak climber" cars in a hurry, firmenauto.de advises charging only below 20 percent.
- Stop at around 80 percent if you want to keep driving. ADAC recommends this because charging beyond that takes disproportionately long. Two shorter stops can be faster overall than one long one; that depends on your car's curve and the spacing of chargers.
- With plateau curves the state of charge is less critical. If your car holds its power for a long time, the remaining charge level is secondary according to firmenauto.de, as long as it is well below 80 percent.
- Warm the battery beforehand. If your car requires it, set the fast charger as the destination in the built-in navigation. In cold weather ADAC advises allowing extra time if you cannot preheat.
- Check the charger's power. A 300 kW charger does not help a car with a 100 kW peak; conversely a 50 kW charger holds back a car with a high peak. The smaller of the two values is the ceiling, and you only reach even that in the favourable part of the curve.
- Avoid shared chargers if an alternative is free. See above: you only get about half the power.
- Know your own curve. firmenauto.de suggests noting power and state of charge at the charger yourself, or looking for charging curves in forums, from manufacturers and from charging providers. Two data points (for example at 20 and at 70 percent) are enough for a first impression.
For ideas on how to spend the time at a fast charger, see Charging break ideas, and for route planning tips see EV road trip tips.
How Elunio handles this
Elunio estimates charging time per station in a simplified way. According to its source code, the app calculates the range from 10 to 80 percent of the battery, adds a charging-loss factor and divides the energy by a constant power: the smaller of the charger's power and the maximum DC charging power of the car you selected (if you selected one). The estimate does not take into account a real charging curve, battery temperature or shared charger power. Because the actual average power cannot exceed peak power, the displayed time is better read as a lower bound; in practice, especially in the cold or at shared chargers, it can take longer. Treat the number as a planning aid, not a guarantee.
What the app offers instead are community reports from drivers on prices, availability and faults. Data is densest in Baden-Württemberg and the wider DACH region; we cannot promise complete coverage. More on the principle in Community prices vs. list prices.
Frequently asked questions
Why does my car charge so slowly from about 80 percent?
According to firmenauto.de, power falls markedly at around 80 percent at the latest for both typical curve types, because the battery management regulates charging to protect the cells. With smaller batteries this can happen earlier.
Is 10 to 80 percent the right yardstick for charging times?
ADAC considers the average charging power between 10 and 80 percent the best basis for comparison and asks manufacturers to quote charging times uniformly in that range. Peak power alone says little about the actual charging duration.
Do I always have to limit charging to 80 percent?
No. For fast charging on the road, 80 percent is often a practical target because charging beyond it takes long. For the battery in everyday use, your model's manufacturer recommendation applies; according to sparneuwagen.de some manufacturers name 80 percent, others regular charging to 100 percent.
Why does my car charge more slowly in winter?
Cold cells limit charging power. ADAC cites examples of 40 to 70 percent longer stops without preheating (Zoe/e-Up about 40, ID.3 about 50, Tesla Model Y about 70 percent).
Why does the app show a shorter charging time than I actually need?
Elunio calculates with constant power (the minimum of charger and vehicle peak power). The real charging curve, temperature and shared chargers are not included.
Conclusion
The charging curve matters more than the peak power on the data sheet: it shows how long your car charges fast and where it drops off. On a long trip the approach that usually pays off is to arrive with a low state of charge, charge preconditioned and move on at around 80 percent, provided the next charger is within range. For everyday use at home, your manufacturer's recommendation applies, not a blanket rule. And for every time estimate, including those in apps, remember that it is a planning aid, not a promise.
Sources: ADAC – "E-Auto Schnellladen: Die besten Modelle für die Langstrecke" (Wolfgang Rudschies, 18 March 2026), adac.de · firmenauto.de – "Was ist eine Ladekurve? Wie lange E-Autos schnell laden" (Holger Holzer, 22 Sept 2021, updated 10 Oct 2024) · sparneuwagen.de – "E-Auto richtig laden: Die 20 bis 80 Prozent Regel im Faktencheck" (24 Sept 2026, changed 7 Oct 2026) · leinetal24.de – "Schnellladen von E-Autos bei Kälte 'problematisch': Laut ADAC bis zu 70 Prozent längere Ladedauer" (2 March 2023; report on an ADAC test of 50 electric cars). The worked example uses assumed values. The description of Elunio's estimate is based on the app's source code (as of 21 Oct 2026).