Field Guide · concept

Battery technology is the set of rechargeable chemistries — most often lithium-ion and lithium-polymer — that store the electrical energy powering phones, wearables, and other portable devices.1

4.2V 3.7V 3.0V full empty state of charge → flat plateau ≈ most of the usable charge steep ↓
A lithium-ion cell holds a long, nearly flat voltage plateau around 3.7 V through most of its charge, then falls sharply near empty — the shape that makes state-of-charge estimation from voltage alone tricky at the ends.

Overview

A battery is rated by capacity (milliamp-hours, mAh, or watt-hours, Wh) and judged on energy density — how much energy fits in a given size and weight — and cycle life, how many charge/discharge cycles it survives before fading. Lithium-ion dominates because it packs high energy density into a light, rechargeable cell with low self-discharge and no memory effect.

Lithium-polymer variants trade the rigid metal can for a flexible pouch that can be shaped to fit thin phones and curved wearables. Charging is managed by control circuitry that balances speed, heat, and long-term wear, since fast charging and high temperatures both accelerate aging. The flat discharge curve above means most of a cell’s energy is delivered at a stable voltage, with sharp knees only when nearly full or nearly empty.

Li-ion vs Li-polymer

The two lithium chemistries share the same electrochemistry but differ in packaging and how that shapes a device:

Property Lithium-ion Lithium-polymer
Package Rigid cylindrical/prismatic can Flexible pouch
Energy density Higher per weight Slightly lower
Shape freedom Fixed forms Thin, curved, custom
Cost Lower Higher
Typical use Laptops, power tools Phones, wearables, drones

The pouch’s shape freedom is why nearly every slim phone and curved smartwatch uses Li-polymer despite the cost.

Where it fits

The battery is the hard constraint that shapes mobile design. A mobile operating system spends much of its effort stretching a charge; a smartwatch or wearable lives or dies by how little its SoC and screen draw. The same power budget explains why a smartphone is a poor host for a continuous SDR decode load like GopherTrunk — sustained CPU and radio use drains a phone fast, where a mains-powered capture node runs indefinitely.

Sources

  1. Lithium-ion battery — Wikipedia, on the chemistry and metrics of modern rechargeable batteries. ↩

See also

Learn it step by step