Battery Degradation Calculator
Every charge cycle costs you a tiny fraction of capacity. Here's the math.
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TimeHealthCapacity
Battery hits 80% health in ~3.2 years
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The 80% Rule: When Batteries Are "Done"
Industry standard: a battery is considered degraded when it reaches 80% of original capacity. Apple guarantees iPhones maintain 80% health after 500 cycles; Tesla warranties 70% after 8 years.
Health after N cycles = 100% × (1 − loss_per_cycle)^N
Typical Battery Degradation Rates
| Device | Loss/100 cycles | Time to 80% |
|---|---|---|
| iPhone (2020+) | ~2% | ~2-3 years |
| Android flagship | ~2-3% | ~2-3 years |
| MacBook (2020+) | ~1.5% | ~3-5 years |
| Tesla Model 3/Y | ~1% | ~8-12 years |
| Laptop (budget) | ~3% | ~1.5-2.5 years |
| Power tools | ~4% | ~1-2 years |
How to Slow Battery Degradation
Charge to 80%, not 100%: Keeping a lithium battery between 20-80% significantly reduces stress. Charging to 100% regularly accelerates degradation by ~30%.
Avoid heat: Battery degradation roughly doubles for every 10°C increase. Don't charge in direct sunlight or under heavy load.
Slow charge when possible: Fast charging generates more heat and stress. Use overnight slow charging for daily use.
Frequently Asked Questions
Modern phones have charge management that stops at 100% and trickle-charges. The bigger concern is heat — if your phone gets warm while charging, use a lighter case or charge on a cool surface.
Deep discharges (below 20%) stress lithium batteries more than shallow cycles. Ideally keep between 20-80%. The "calibration" myth (fully discharge monthly) is outdated for modern lithium batteries.
As of 2024: $5,000-$15,000 for most EVs. Tesla battery packs run $5,000-$13,000 depending on model. Costs are declining ~10-15% per year as manufacturing scales.
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