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A battery will release its charge when a circuit is completed between its positive and negative terminals. If you store batteries in a container alongside other metal objects, there is a risk of a short circuit that can trigger an accidental discharge.
Typical cylindrical batteries, such as those found in remote controls or flashlights, have terminals located at opposite ends. Because the terminals are separated, accidental short‑circuiting is less likely; a complete loop must be formed for current to flow. However, when these batteries are stored together with metallic items—keys, coins, or silverware—contact between a terminal and a metal piece can create a conductive bridge, gradually draining the battery and potentially causing damage or leakage.
Nine‑volt batteries present a higher risk because both terminals are exposed on the top of the casing. This configuration makes it easier for accidental contact to connect the positive and negative ends. Manufacturers therefore ship nine‑volt batteries with a plastic cap covering the terminals to prevent short circuits during storage and handling.
