Battery and LED pages exist for learning and low-voltage planning. They multiply capacity by load assumptions or compute a series resistor from voltage headroom—they do not approve building wiring.

Runtime tools divide usable capacity by load current (or energy by watts). Capacity tools rearrange the same relationships. Real packs derate under cold, high drain, and aging—enter conservative numbers.

The LED worksheet uses Ohm’s law on the leftover voltage after forward drops. Cross-check resistor wattage. For Ohm’s law practice on resistive loads, open the Ohm’s law calculator next—and read the safety blog before any mains work.