How may thermal runaway be prevented?

• A. By using a hydrometer
• B. By carefully monitoring the temperature of the middle cells and controlling the charging current
• C. By discharging completely
• D. By increasing charging current

Answer: (B)

Preventing thermal runaway comes down to keeping heat in check by watching cell temperatures and dialing back the charge as needed. If a cell or a group of cells heats up, that heat can accelerate chemical reactions inside the cells, generating more heat in a dangerous feedback loop. By carefully monitoring the temperature of the cells—especially the middle cells in a series pack where temperature rise can be most pronounced—and reducing or stopping charging current when temperatures rise, you limit heat generation and give cooling systems a chance to remove it. This is why controlling charging current based on temperature is the most effective preventive measure.

Hydrometer is for measuring specific gravity in lead-acid batteries and isn’t applicable for preventing thermal runaway in modern chemistries. Discharging completely won’t reliably prevent runaway and can be risky while not addressing the underlying heat generation. Increasing charging current would raise heat and worsen the problem.