Thank you for your question, Evlover
One of the most persistent—and unfortunately still widespread—myths is that fully charging or deeply discharging lithium batteries harms them, and they should always stay at around 50%. I don’t know who promotes this idea, but it’s simply not true! Please, don’t believe it for a second.
In lithium batteries, a lithium-ion migrates through a semi-permeable membrane and, when charged, nests comfortably in the gaps of a graphite lattice. When discharged, it becomes part of a compound complex. It’s not like we’re pumping air into the battery, causing harm from overpressure; the lithium-ion simply moves from one place to another under a small electrical potential of just 3–4V. As such, fully charging or discharging does not harm any
lithium battery.
For ternary cells, the operating range is typically 2.5–2.7V to 4.2V (for LFP cells, it’s 2.00V to 3.65V). This represents the total battery capacity physically built into the vehicle. However, for s
afety reasons, manufacturers cut off a portion of this range at both ends, so it’s common for cells to only operate between 3.35V and 4.16V (LFP: 2.8V to 3.6V), which is called the "net" or usable battery capacity.
In the case of the
Hyundai Ioniq with a 28 kWh battery, there have already been reports of cars suffering reduced capacity because they were managed using the "smart" 20–80% strategy. Similarly, the Bolloré BlueCar models are regularly repaired due to the damage caused by this supposedly "battery-friendly" wisdom. Every day, the list of victims grows.
The
Tesla Model Y with an LFP battery will be the next victim if you don’t follow
Tesla's guidance and instead listen to internet "armchair experts." The LFP battery's characteristics are such that the cell voltage doesn’t increase noticeably until the charge level reaches 99%. At that point, the voltage suddenly jumps by as much as 0.25V in seconds. This leaves the BMS (Battery Management System) with insufficient time to balance the cells, as it can only adjust their voltage in the last 3–5 minutes of charging. This is why it’s crucial to
always charge LFP battery vehicles to 100%, not just 80%.
Moreover, the fear of charging to 100% is baseless because the unique properties of LFP chemistry cause the cell voltage to drop back down by 0.25V within just 15 minutes of reaching 100%. This means that even when the battery is at 99% charge, the "voltage stress" on the cells is exactly the same as it would be at 20% charge.
The one part I disagree with is the recommendation to "leave your vehicle plugged in." This might work in the
U.S., but for everyday use, there’s no need to leave it constantly plugged in. Charge it during the day as needed (it doesn’t always need to be charged to 100%), but when you get home in the evening, plug it in and let it charge fully to 100%. Once charging is complete (or the next morning), unplug it. There’s no point in recharging every night if you come home with, say, 60–80% charge and have enough range for the next day. Use the entire battery range, as you paid for the bottom of the battery too, not just the top!
Think of it like a gas-powered car: if you don’t have enough fuel for the next day, you fill up before heading home—but you don’t detour to the gas station every night just to keep the tank full. Manufacturers optimize charging systems for typical usage patterns, not the pseudo-science of armchair experts.
If the car will be unused for several weeks or months, then it does make sense not to leave the battery at 100%. In such cases, there are specific steps to follow, which I’ve explained in previous answers. For your situation, charging to 100% once a week is sufficient.
Best,
Battery Doctor
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