Modular, Safe, User-Replaceable Battery Power Bank

The core opportunity here stems from the user's concern about 'spicy pillows' (swollen lithium-ion batteries) and the expressed desire for gadgets using standard, replaceable batteries. A product designed as a modular power bank, allowing users to insert and replace standard rechargeable cells (e.g., 18650, 21700, or even AA/AAA for lower power), would directly address safety concerns, extend product lifespan, and reduce electronic waste. The product would consist of a durable casing with a charging/discharge circuit and slots for user-provided or branded replaceable batteries. This offers users peace of mind regarding battery safety and longevity, differentiating it from traditional sealed power banks.