Battery life and performance is influenced by temperature. Internal heat generation occurs in the lead acid cell during charge and discharge.
The typical heat evolution in a flooded 588 Ah (C₁₀) lead acid battery is shown below.


In VRLA batteries a lower end-of-charge voltage is used (2.22 to 2.28 Vpc). Hence a reduced heat evolution is expected. However the internal oxygen recombination reaction is a new and additional source of heat, generating approximately 0.09 Watt power per cell and 100Ah/C₁₀ capacity.
The heat evolution differential between a 100 Ah/C₁₀ flooded and VRLA cell in float service is shown below.



The waste-heat generation Q is given by the following formula: Q=0.77 x number of cells x current (A) x hours (watt hours) Good operating practice of batteries requires an efficient heat removal (see section 5) specifically with VRLA types. Heat stagnation can cause thermal runaway. Thermal runaway is a critical condition arising during constant voltage charging in which the current and the temperature of a battery produce a cumulative mutually reinforcing effect which further increases them and can lead to the destruction of the battery.