What is a thermal runaway?

The appropriate charge voltage depends on the battery temperature. A warmer battery requires a reduced voltage. If the voltage is not reduced, then the current accepted by the battery increases. When the current increases, then heating within the battery increases. This can continue in a loop, feeding on itself with the battery temperature and charging current rising to destructive levels. This is thermal runaway. Batteries may become more susceptible with increasing age. Without a recombination reaction, flooded batteries convert most excess charging energy to gas, not heat. This makes them almost immune from thermal runaways.

Thermal runaway can be prevented with the following:

  • Temperature compensation monitoring at the battery and not at the charger
  • Limiting charging currents to appropriate levels
  • Allowing for adequate air circulation around the batteries
  • Using timers, or Ampere-hour counters
  • Using smart chargers that recognize the signature of a thermal runaway will shut the charger down