Usually yes. A quality power bank with built-in protection circuitry can charge safely overnight; heat and cheap, uncertified units are the actual risk.
Power banks are just larger lithium-ion batteries with their own charging and protection circuit, so most of the same rules that apply to phones apply here, with one added factor: they're often tucked into bags or drawers with poor airflow.
The brand and build quality of the power bank matters more than the number of hours it spends plugged in.
Reputable power banks include a battery management circuit that stops charging once the cells reach full, similar to a phone. This prevents the constant overcharging that damaged batteries in some early, poorly regulated devices.
Swelling or a puffed-out case, an unusual smell, a port that feels hot to the touch, or noticeably slower charging than usual are all signs to stop using the power bank and dispose of it properly rather than keep charging it.
No-name power banks without safety certification are more often linked to overheating incidents than banks from established brands. Pair it with an undamaged cable, a fraying cable is a bigger risk than the hours spent charging.
Charge it on a hard, open surface, not fabric, away from direct sunlight, and check on it occasionally if it's new or unfamiliar. After the first few charge cycles, most reputable units are predictable and safe to leave overnight.
A well-made power bank handles overnight charging fine. Keep it on an open surface away from heat, and retire it at the first sign of swelling or an unusual smell.
It's rare with certified, well-made units, but cheap uncertified power banks or damaged cells carry a higher risk of overheating.
Mild warmth is normal; if it feels hot to the touch, smells odd, or swells, stop using it immediately.
It works on many models, but it generates more heat than one task alone, so keep it on a hard surface with airflow if you do this.
Most hold up well for a few hundred charge cycles, roughly 2-4 years of regular use, before capacity noticeably declines.