If you spend any time in EV communities, you will quickly encounter the 80% rule: charge to 80% on DC fast chargers and move on. Some drivers follow it religiously. Others dismiss it as overcaution. Most know it is a thing without quite knowing why.
The reason is worth understanding — because it is actually several reasons stacked on top of each other, and they all point the same direction.
The chemistry
EV batteries are not like fuel tanks. You cannot fill them at a constant rate until they are full.
During a DC fast charging session, the charging curve (the rate of power delivery plotted against the battery’s state of charge) tells the real story. From around 10% to 80% SoC, most EVs accept charge at or near their peak rate. A 150 kW vehicle charges at close to 150 kW. Things move quickly.
At around 80%, the Battery Management System begins tapering the charge rate. For NMC and NCA chemistries (used in most non-Chinese EVs), the electrochemistry above 80% becomes sensitive to a phenomenon called lithium plating, where lithium ions deposit on the anode surface instead of intercalating cleanly. Charge too fast at high SoC and you degrade the cell. The BMS knows this, so it throttles back.
The practical result: the last 20% of charge takes approximately as long as the previous 60%. Charging from 20% to 80% might take 25 minutes. Charging from 80% to 100% might take another 20–25 minutes — for a range addition less than a third as large.
The maths on the road
If you are on a long trip with multiple charging stops, this asymmetry compounds.
Stopping at 80% each time and pushing on to the next charger means you move faster and charge more often but briefly. Waiting for 100% at each stop means longer pauses with diminishing returns. Route planning apps like ABRP account for charging curves per vehicle model in their time estimates: optimal plans almost never include 100% charges unless the next segment demands it.
The rule of thumb: arrive at each charger as low as you comfortably can; leave at 80% or whatever the next leg requires, whichever is higher.
The exception: LFP batteries
LFP (lithium iron phosphate) batteries have a different electrochemical profile. They are more tolerant of high-SoC charging and, importantly, their Battery Management System actually requires periodic full 100% charges to calibrate the SoC display. Without that calibration, the estimated remaining range drifts.
If your EV uses an LFP battery (common in BYD vehicles, some Teslas, and most Chinese EVs), the advice from most manufacturers is to charge to 100% regularly at home. On a fast charger during a trip, the 80% logic still applies for time efficiency. Guilt-free 100% home charging is the recommendation, not the exception.
The pricing signal
On top of the chemistry, there is now a financial signal reinforcing the same behaviour.
At busy highway Superchargers (including the Coolac NSW site on the Hume Highway), Tesla applies a congestion fee of $0.50 per minute once your battery exceeds 80% SoC and the site is marked as busy. The fee also accrues if you are plugged in but have stopped charging.
This is not arbitrary. The congestion fee is a direct translation of the charging curve into financial terms. Charging from 80% to 100% occupies a stall for roughly the same time as charging from 10% to 80% — but delivers far less energy and range. At a congested site, that last 20% costs one driver very little extra while potentially delaying several others.
At 750 kW of total site capacity, a Coolac Supercharger cycling drivers through at 80% can serve roughly 13 vehicles per hour, each leaving with about 300 kilometres of range. If even a handful of vehicles top to 100%, throughput falls. The congestion pricing is designed to make the maths visible in real time.
What actually happens at Easter
The Easter 2026 queues at highway Superchargers were covered extensively, mostly as evidence that EV infrastructure has failed. The reality is more nuanced.
One thing is clear from the per-minute occupancy data: the sites were at capacity. Every extra minute a vehicle occupied a stall above 80% SoC was a minute of delay for someone in the queue. Congestion pricing helps, but it cannot override the physics. The most effective tool at a congested site is collective behaviour: drivers who understand the charging curve and act on it.
The practical summary
- NMC/NCA batteries: stop at 80% on fast chargers during road trips; charge to 80–90% at home routinely
- LFP batteries: charge to 100% regularly at home for calibration; still stop at 80% on fast chargers for time efficiency
- At a busy site: 80% is not just efficient — it is considerate; the next person in line will thank you
- Planning apps: use ABRP or similar; let the charging curve per vehicle inform the plan, not intuition
The 80% rule survives scrutiny because it is not a rule at all — it is just what the chemistry, the maths, and the economics all independently recommend.
