What Is a Battery? (And Why It Matters for Your Phone)

We talk about batteries every day — dead ones, swollen ones, brand-new ones — but what is a phone battery, really?

Here’s what’s hiding inside that sleek metal case and why it plays a bigger role than most people realise.

Inside Every Smartphone Battery

Most modern phones use lithium-ion batteries — lightweight, rechargeable power packs that can store a lot of energy for their size.

Each one is made up of:

• Cells: Where the chemical reaction that stores energy happens.

• Electrodes: Positive and negative sides that move charge during use and charging.

• Electrolyte: A liquid or gel that helps ions move between the two sides.

• Protection circuit: Keeps everything safe, preventing overcharging or overheating.

How It Works

When you charge your phone, electricity moves into the battery and rearranges its internal chemistry.

When you use your phone, that energy flows back out as electrical current — powering your screen, processor, camera, and everything else.

Each full charge and discharge counts as one cycle.

Over hundreds of cycles, the battery slowly loses its ability to hold the same charge — that’s why older phones run out faster.

Why Batteries Wear Out

Batteries are a bit like humans: the more they work, the more tired they get.

Heat, heavy use, and frequent fast-charging all accelerate wear.

After about 500 cycles (roughly two years of daily use), most iPhone and Samsung batteries start showing noticeable decline.

When to Replace It

If your phone’s dying faster, running hot, or showing battery health below 80%, it’s probably time for a replacement.

A new battery restores performance, improves charging speed, and can extend your phone’s life by years.

At Phone Repair NZ, we replace batteries in most iPhone and Samsung models within two hours or less, using quality-tested parts backed by a six-month warranty.