Why don’t phones and laptops have power sources that never run out?

A device can’t produce energy forever without getting energy from somewhere. The second law of thermodynamics rules out a genuinely perpetual power source. Batteries are simply a practical way to store energy until the device needs it.

If a computer stays in one place, you can avoid batteries by plugging it into the wall. Phones and laptops need to work while being carried around, though, so they need either stored energy or a reliable wireless power source.

Some low-power devices already work without conventional batteries. Solar calculators, RFID cards, and crystal radios harvest energy from light or nearby radio waves. The issue is power density: phones and laptops need far more energy than those systems can conveniently collect.

Long-lasting nuclear or radioactive power sources do exist, but they’re unsuitable for ordinary consumer electronics. They can involve radiation hazards, strict regulation, safety concerns, and enough energy to create serious problems if misused. For now, rechargeable batteries are much safer and more practical.