Tenergy 1.5 Volt Battery LR44, Button Cell LR44, ag13/LR44 Batteries Equivalent, Ideal for Watches, Laser Pointers, Small Toys, Portable Electronics, and More, 20 Count

Customers find these batteries work well in fairy lights and have a perfect fit. The battery life receives mixed feedback - while some say they last a year, others report they don't last long at all. The brightness also gets mixed reviews, with several customers finding them bright, though one notes the light becomes barely visible over time.