How does temperature affect battery voltage?
As the temperature increases, the equilibrium voltage of the lead acid battery, EMF, or open circuit voltage also increases. This is 2.5 millivolts per °C
when electrolytes have the specific gravity range commonly used in lead-acid batteries. Another factor that affects blood pressure is acid sp gr. With increasing temperature, the acid expands and sp gr decreases. The extension is about 5%. This is the reason for the decrease in specific gravity. Based on the above 2 factors, the change (correction) in OCV is 3 millivolts/degree Celsius (mV/°C)
This is of concern when the electrolyte temperature exceeds 25-27 °C to 35°C and higher. The charging voltage should be set to a lower value, i.e. reduce the charging voltage by 3 mV for every 1 °C rise above 27 °C. Otherwise, battery life will be reduced due to higher gas content and network corrosion. At higher temperatures the float voltage decreases and at colder temperatures increase the float voltage 3 mV per °C