Batteries & power management

In one line

A battery stores a fixed amount of energy (its capacity, in milliamp-hours). Runtime is capacity divided by current draw — so low power is a design goal, not an afterthought.

<figure style="text-align:center;margin:1.5rem 0"> <svg viewBox="0 0 300 110" role="img" aria-label="Battery symbol feeding a device" style="width:100%;max-width:330px;height:auto;color:var(--c-iot)"> <line x1="20" y1="55" x2="70" y2="55" stroke="currentColor" stroke-width="2"/> <line x1="70" y1="35" x2="70" y2="75" stroke="currentColor" stroke-width="4"/> <line x1="84" y1="44" x2="84" y2="66" stroke="currentColor" stroke-width="2"/> <line x1="98" y1="35" x2="98" y2="75" stroke="currentColor" stroke-width="4"/> <line x1="112" y1="44" x2="112" y2="66" stroke="currentColor" stroke-width="2"/> <line x1="112" y1="55" x2="170" y2="55" stroke="currentColor" stroke-width="2"/> <text x="64" y="30" font-size="13" fill="currentColor" text-anchor="middle">+</text> <text x="120" y="30" font-size="13" fill="currentColor" text-anchor="middle">−</text> <rect x="170" y="38" width="70" height="34" rx="5" fill="none" stroke="currentColor" stroke-width="2"/> <text x="205" y="59" font-size="10.5" fill="currentColor" text-anchor="middle">device</text> <text x="150" y="100" font-size="10.5" fill="var(--text-3)" text-anchor="middle">runtime = capacity (mAh) / current draw (mA)</text> </svg> </figure>

How it works

Designers manage a power budget and spend most of the time asleep.

• Sleep & wake — an MCU spends 99%+ of its life in a microamp sleep, waking briefly. A coin-cell sensor can last years.
• Efficient conversion — switching regulators (built around an inductor) step voltage with little waste.
• Chemistry — lithium primary cells for decade-long implants; lithium-ion for wearables.

Where it shows up in digital health

• Pacemakers & ICDs run 7–15 years on one lithium cell — every microamp saved is months of patient benefit.
• Wearables & patches trade battery size against runtime.
• Wireless recharging (via an inductor) avoids a wire through the skin.

Watch for

Lithium cells store a lot of energy — abuse risks fire. Medical battery design carries safety standards (IEC 62133), and "low battery" handling is a clinical requirement.