New Delhi, Nov. 3 -- For years, smartphone owners were told not to leave their devices plugged in too long or their battery would suffer. But today, Apple, Samsung and Google say that fear belongs to the past. Thanks to smarter charging systems built into modern phones, plugging in overnight or all day is no longer harmful like it once was.

Instead, the major concern has shifted to something else entirely: heat.

Lithium-ion batteries are designed to stop receiving full power once they reach 100%. Smartphones now pause or slow charging once that point is reached, topping up only when needed. This prevents the stress that caused damage in older devices.

Still, battery health naturally declines over time. The faster a battery wears down d...