You should completely drain your phone or laptop battery before plugging it in to recharge, to preserve battery health.
This myth originated from older nickel-cadmium batteries, which developed 'memory effect' and benefited from full discharge cycles. Lithium-ion batteries, standard in modern devices since the 1990s, operate oppositely: repeated deep discharges and full charges stress the chemical cells and reduce lifespan. Battery longevity peaks with partial charge cycles (e.g., 20–80%) and avoiding extremes; most modern devices include charge management that caps charging at 80% during idle periods or implements smart charging features. Apple, Tesla, and battery researchers consistently recommend avoiding depleting below 20% and preventing consistent full charges to maximise years of service.