EL
BG
DE
ES
FR
ITGlossary · Batteries
Thermal Runaway
An uncontrolled temperature rise in a battery, where heat speeds up currents or reactions that produce even more heat.
Technical level:Advanced
In VRLA lead-acid batteries it usually starts in a hot room or with too high a charging voltage. The heat raises the charging current, which heats the battery further, and the cycle repeats until the battery swells, dries out or vents gas. In lithium batteries, an internal short circuit or damage can lead to fire, although LiFePO4 batteries are far more resistant than other chemistries.
Prevention relies on a temperature-compensated charger, good ventilation, the right room temperature and a properly working BMS.
If you see a swollen or unusually hot battery, stop charging safely and replace it. Do not use it again.
Related terms
- Fast ChargingA charging method that restores battery capacity quickly without damage by controlling current, voltage and temperature.
- Depth of Discharge (DoD)The share of a battery's capacity that has been drawn in a discharge, where 100% means fully discharged.
- Ampere-hour (Ah)The unit of battery capacity, showing how much current a battery can deliver and for how long, e.g. 9 Ah means 0.45 A for 20 hours.
- Battery Charging CurrentThe amount of current supplied to charge a battery, regulated by the UPS system.
- Battery Management System (BMS)A system that monitors and manages the performance, health, and charging of batteries.
- Battery Service LifeThe years a battery keeps enough capacity, typically 3–5 years for VRLA at 20–25 °C, shortened by high temperatures.