You commented BATTERY. Here's the switch on every device, the papers behind the reel, and what the "AI" in your laptop actually does. Every claim links to its source.
1. The switch, by device
iPhone 15 and later: Settings → Battery → Charging. Pick a limit between 80% and 100% in 5% steps. At 100%, Optimized Battery Charging is on by default. Apple
iPhone 14 and earlier: Settings → Battery → Battery Health & Charging → Optimized Battery Charging. Apple: "Turning off charging optimizations can increase wear on your battery and reduce its lifespan." Apple
Mac: System Settings → Battery → the info button next to Charging → Optimized Battery Charging. Apple's page does not state whether it is on by default, so check. A manual Charge Limit (80% to 100%) exists too, but only on macOS Tahoe 26.4 or later with Apple silicon. Either way, "your Mac will occasionally charge to 100% to maintain accurate battery state-of-charge estimates." Apple
Pixel: Settings → Battery → Battery health → Charging optimization. Adaptive Charging learns your habits (it needs about 14 days), or tap Limit to 80%. Google
Chromebook: Optimized charging. Google: "your Chromebook uses machine learning" to predict your unplug time. Google
Windows (any brand): Smart charging exists only where "some device manufacturers turn on Smart charging in Windows 11", and each maker implements it differently. When it is on, the battery icon shows a heart; from February 2026 on Windows 11 24H2+, HP says the heart has been replaced by a plug icon. Microsoft · HP
Surface: smart charging is always active and "limits its maximum charge to 80%" when it detects long plug-in periods or heat. Microsoft
ASUS: MyASUS → Battery Health Charging. Full Capacity is the default. Balanced stops at 80%, Maximum Lifespan at 60%. ASUS
Lenovo: Conservation Mode (Lenovo Vantage). The Legion guide: "the battery's charge will be kept within 75%–80%". Lenovo
HP (business notebooks): HP Battery Health Manager, set in the BIOS setup. "Maximize Battery Health" limits the full charge to 80%; the default is "Let HP Manage My Battery Health". HP
Dell: Dell Power Manager → Battery settings. "Primarily AC" lowers the threshold "so that the battery never charges to 100 percent capacity" (Dell publishes no percentage); "Adaptive" adjusts to your patterns. Dell
2. Why sitting full wears it out
The ions. When you use the battery, lithium ions flow from the anode to the cathode; when you charge, they flow back. Nobel Prize in Chemistry 2019
The film. The electrolyte reacts with the lithiated graphite anode and forms an SEI layer. "The compounds in the SEI contain lithium, trapping it and preventing it from participating in charge storage; an effect known as loss of lithium inventory." Its ionic resistance is higher than the electrolyte's, so the remaining ions move slower. O'Kane et al., arXiv 2112.02037
Full charge drives it. "Lower anode potentials, which aggravate electrolyte reduction and thus promote solid electrolyte interphase growth, have been identified as the main driver of capacity fade during storage. ... To maximize battery life, high storage SoCs corresponding to low anode potential should be avoided." Keil et al., J. Electrochem. Soc. 163 (2016)
The 100% vs 80% result. A storage study at KIT (Karlsruhe): "A large impact of the storage state of charge at 100% is evident, whereas the influence is small below 80%", and fade accelerates with temperature "following the law of Arrhenius". Honest limit: that is a graphite/NCA pouch cell in a lab, not a laptop pack. Werner, Paarmann, Wetzel, Batteries 2021
Heat. Apple: avoid ambient temperatures above 35 °C (95 °F), "which can permanently damage battery capacity". Apple
Plugged in at 100% is not overcharging. Dell: the laptop "is designed to stop charging once the battery reaches full capacity. After that, your laptop runs directly on power from the AC adapter". The charger chip terminates the charge at the end of the cycle and the system keeps running without the battery. One exception: some Alienware, Precision and G Series gaming/workstation models can still draw from the battery under heavy load while plugged in. Dell FAQ · TI BQ25672 datasheet · Dell hybrid power
What I could not source: a hard "20 to 80%" window (no primary paper names one; the closest is the KIT line above), and a headline percentage for how much faster a full battery fades. Battery University's table estimates 96% capacity after a year at 25 °C and 40% charge versus 80% at 100% charge, but that is a secondary source, so treat it as direction, not a number to repeat. Battery University BU-808
3. What the AI actually does
Stopping the charge is not the same as being at a safe level. A laptop that stops at 100% still sits at 100%. So parking it lower is a prediction job, and Apple describes it in those terms: Optimized Battery Charging "uses on-device machine learning to learn your daily charging routine so that it can delay charging past 80% in certain situations, such as when it predicts that your Mac will be connected to power for an extended period of time." The iPhone page uses the same wording. Google says "machine learning" for Chromebook and "learning your charging habits" for Pixel. The cost, in Apple's words: it will still occasionally charge to 100% to keep its estimate accurate, and HP and Surface both say a cap means less runtime on battery.
4. The three habits
Turn the mode on for your device from the list above. If your Windows laptop has no such mode, it has no 80% logic; that is the case the fix cannot help.
Keep it cool. 35 °C ambient is Apple's line. A closed laptop on a duvet or in a hot car is where the heat damage happens.
Run it on battery now and then. Dell's own FAQ: "it is a good idea to use your laptop on battery power occasionally rather than keeping it plugged in".
Mike
PS: Want more like this, how the tech you use every day actually works? You're already on the list. Reply and tell me what to break down next.