Why does one person swear charging to 100% is fine and another says it kills the battery?

Why does one person swear charging to 100% is fine and another says it kills the battery?

It's one of the oldest arguments in the EV world. Your neighbor charges his car to 100% every night and swears that, three years on, the battery is perfect. You hop onto a forum and half the thread tells you you're torching your investment—never go past 80%. So who's right?

The uncomfortable answer is: both of them. And not because it's a matter of opinion, but because they almost certainly have batteries with different chemistries. The right advice for one is exactly the wrong advice for the other. Let's settle this once and for all—and bring it down to earth for what actually matters in Costa Rica and the region.

First: which battery do you have?

Nearly every EV on the road today uses one of two chemistry families, and they're cared for differently:

• LFP (lithium iron phosphate). Very common in Chinese brands—BYD's "Blade" is LFP (BYD)—and in standard-range Teslas. More forgiving, safer, handles more cycles; in exchange, it stores a little less energy per kilo.
• NMC / NCA (nickel-based). The higher energy density option: more range. You'll find it in the VW ID.4, the Hyundai/Kia lineup, and long-range Teslas, for example. More sensitive to abuse.

(The Nissan Leaf is its own special case: it uses a manganese-based chemistry, not LFP, and we'll come back to it because in hot climates it has one important quirk.)

Not sure which one you've got? There's a simple trick on Teslas: if the charge control shows "50% / 100%," it's LFP; if it shows "Daily / Trip," it isn't (Tesla). On other brands, check the model spec sheet or ask at the shop—and if your EV is a BYD, it's almost certainly LFP.

LFP chemistry: charge to 100% with a clear conscience (in fact, you should)

Here's the surprise for a lot of people: if your battery is LFP, charging to 100% isn't just allowed, the manufacturers recommend it. Tesla, for one, advises keeping the charge limit at 100% even for daily use on its LFP cars, and hitting 100% at least once a week (Tesla).

Why? Because of a physical oddity of LFP: its voltage curve is extremely flat across the middle of the charge range. The voltage barely changes between 30% and 80%, so the battery's brain (the BMS) loses precision figuring out how much charge is left—the errors can top 15% (accure). Taking it to 100% every so often gives the BMS a firm reference point to recalibrate against.

One thing to keep straight: charging an LFP to 100% recalibrates the reading, it doesn't "heal" the battery. It won't give back lost capacity; it just makes the range gauge trustworthy again. But yes—on an LFP, the fear of 100% is unfounded.

"The 80% rule is a dogma inherited from the NMC world. But chemistry doesn't answer to dogma: an LFP is built to live full—charge it to 100% guilt-free." — Alonso Aguilar, Founder & CEO

NMC / NCA chemistry: here, the daily 80% rule does make sense

If your battery is nickel-based, the classic advice applies. Leaving the battery sitting near 100% for long stretches accelerates calendar aging: the higher the state of charge at rest, the faster the internal layer that keeps trapping lithium grows. Long-term aging studies confirm it: the capacity loss from storing at 100% is considerably higher than storing at 80–90% (Frie et al., ChemElectroChem, 2024). That's why manufacturers recommend leaving the daily limit at ~80% and saving the full 100% for travel days (Tesla).

Important: 80% isn't a magic cliff—degradation rises gradually with state of charge, it doesn't "spike" right at 81%. It's a good rule of thumb, not a law of physics.

A reality check: don't obsess over the percentages

Before you start living your life counting charge points, here's a fact that should put you at ease. The fleet study by Geotab, covering 22,700 vehicles, found that for normal use the strict 20–80% rule is usually unnecessary. The reason? Manufacturers already build in hidden software "buffers": the 100% you see on the screen is chemically less than a full cell, and the 0% isn't a truly empty cell.

Degradation only accelerates noticeably when the car spends more than 80% of its time parked near full or near empty. In Geotab's numbers: low exposure to the extremes, 1.4% loss per year; high exposure, 2.0%. Useful to know, but not worth losing sleep over. Charge however suits you; just avoid leaving the car at 100% (or 5%) for weeks on end without moving.

Time parked near full or empty → annual loss

Less than 50% of the time

1.4%

Between 50% and 80%

1.5%

More than 80% of the time

2.0%

fleet of 22,700 EVs · Geotab 2025

The real enemy in LATAM isn't the percentage: it's the heat

Here's the twist that changes the whole conversation for our region. While the rest of the world debates 80 versus 100, the factor that truly rules in hot climates is temperature—and it turns critical when it's paired with a high state of charge.

The technical reference is blunt: the worst situation for a lithium battery is keeping it fully charged at elevated temperature. Under lab conditions, a full cell stored continuously at 40 °C can lose close to 35% of its capacity in a single year, versus just ~6% at 25 °C with a partial charge (Battery University, BU-808). It's an extreme-stress figure—not what happens to your car in everyday use—but it shows the direction: heat + full charge = the worst combination.

For Costa Rica this is directly practical. The country is one of the region's leaders in EV adoption—with record market share and a strong presence of Chinese brands like BYD (Tico Times)—but it has two climate worlds: the hot coast of Guanacaste and the Pacific, and the much cooler Central Valley and the mountains. An EV that lives under the coastal sun faces a faster aging clock than one up in the highlands.

What to do about it, whatever chemistry you have:

• Park in the shade whenever you can. It's probably the single best thing you can do for your battery in the tropics.
• Don't leave the car at 100% under the sun for hours. If you have NMC, charge to 80% for day-to-day; if you have LFP, the percentage isn't as critical, but still avoid the full-plus-prolonged-heat combination.
• If you charge overnight to head out in the morning, schedule the charge to finish close to the time you'll use it, instead of sitting full and hot all afternoon.

The used Nissan Leaf case (pay attention on the coast)

If you're eyeing a used Leaf in a hot area, pay attention. First- and second-generation Leafs (through 2024) use passive air cooling, with no active thermal management system—unlike nearly every modern EV, which cools the pack with liquid. That makes them degrade noticeably faster in hot climates (Battery University, BU-1003a). A Leaf that spent its life in Guanacaste is not the same as one from the Central Valley. It's not a bad car—but it's exactly the case where a battery scan before you buy is worth double.

Fast charging and the cold: two final notes

Fast charging (DC): use it without guilt whenever you need it. What does take a toll is depending on it every single day. Geotab measured that cars relying heavily on high-power fast charging degrade roughly twice as fast as those that use it occasionally (3.0% vs 1.5% per year). A practical tip: don't push fast charging past 80%—above that it charges painfully slowly and just adds heat for little benefit.

Cold (for the highlands): if you fast-charge with a very cold battery—more likely on a mountain dawn than on the coast—the lithium can plate out as metal instead of slotting into the electrode, a largely irreversible kind of damage called plating (Battery University, BU-410). That's why many cars "precondition" (warm) the battery before a fast charge. In the tropics it's a smaller problem than the heat, but it's worth knowing.

Your quick charging guide, by chemistry

(The Nissan Leaf uses a manganese-based chemistry, neither LFP nor properly NMC, and with no liquid cooling through 2024—treat its thermal care with extra caution in hot climates.)

The one thing that tells you whether your habits are working

Here's the honest close. All of this advice moves the needle, but none of it tells you by how much—because the wear is invisible. You can baby the battery by the book and never notice the difference, or abuse it and not find out until the range has already dropped a fair bit.

The only way to know whether what you're doing is working is to measure your battery's health over time. One scan gives you today's status; several scans in your electric's passport give you the trend—the real proof of whether your habits (and your climate) are protecting or burning through your investment.

"We love giving charging advice, but we're the first to say don't stop at the theory. Measure. Your battery, in your climate, with the way you drive, will tell you the truth better than any one-size-fits-all rule off the internet." — Alonso Aguilar

So the next time someone tells you with total confidence that charging to 100% "always" ruins the battery, you've got the grown-up answer ready: it depends on your chemistry, and in the tropics, it depends above all on the heat.

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Want to know whether your charging habits are protecting your battery? Start your electric's passport with a scan and track its health over time. Try the SOHpro simulator or learn more at SOHpro.