WHERE CAPACITY GOES

The main aging mechanisms

🧩

SEI growth Slowly eats lithium and adds resistance, faster when hot or full

Lithium plating Metal lithium on the anode from fast or cold charging

Particle cracking Swelling and shrinking break cathode and silicon particles

Metal dissolution Manganese or nickel leaches out of the cathode and poisons the anode

Electrolyte loss Side reactions slowly use up the liquid and make gas

Aging is many small reactions adding up.

TRY IT

How you use a cell sets how long it lasts

Change the depth of each discharge, the temperature and the charge rate and watch how many cycles the cell lasts.

Heat, deep cycles and fast charging all speed up wear.

TWO CLOCKS

Calendar aging and cycle aging

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Calendar aging

Happens even on the shelf: worst when hot and full

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Cycle aging

Happens with use: worst with deep, fast cycles

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Real life

A car parked most of the day ages mostly by the calendar

Cells age whether you use them or not.

THE SIGNS

How aging shows up

🔎

Capacity falls (less range, shorter run time) and resistance rises (more voltage sag and heat under load). Many warranties and standards call a cell worn out at 70–80% of its original capacity.

An old battery is both smaller and weaker.

LONG LIFE

Habits that help

💚

🌡️

Avoid heat

Don't leave devices in hot cars or in the sun

🔋

Stay in the middle

Store around 40–60% charge; avoid sitting at 100% for long

🐢

Charge gently when you can

Use fast charging when you need it, not always

Most phones and cars now manage this for you with charge limits.

UNIT 16 STUDY COMPLETE

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Ready for the Fab Challenge?

You've seen what wears a cell out and which habits help it last.