TL;DR
Drop an AA or AAA battery from 5–10 cm onto a hard surface: if it bounces noticeably, it's likely dead. If it stays put, it's still charged.
Season: All year
 ## How to do it 1. **Hold the battery upright** — positive end up. 2. **Drop it from about 5–10 cm** onto a hard, flat surface (table, tile). 3. **Read the result:** - 🟢 **Stays upright / barely tips** → likely full. - 🔴 **Bounces noticeably** → likely dead. ## Why it works As an alkaline battery discharges, its internal chemistry changes: the gel-like paste solidifies (partly due to zinc oxide forming). A **full** battery absorbs the impact — a **dead** one bounces back. ## Good to know - Works reliably with **alkaline batteries** (AA, AAA). Lithium and rechargeable cells behave differently. - This is a quick check — for critical devices, use a multimeter. - When in doubt: test several batteries side by side and compare.