The Narada REXC lead-carbon batteries have lower charge voltage settings than traditional flooded lead-acid batteries, and even slightly lower voltages than GEL batteries which are less than flooded batteries. This is because lead-carbon batteries have a lower internal resistance than other lead-acid battery types due to the highly conductive carbon in the negative electrode. This means it requires slightly lower voltages to drive the charge current and also means that charge currents can be higher than other lead-acid battery types without generating so much heat which can damage other battery types.
To put it in terms of a 12V battery which many people are used to from their experience with car batteries, a normal bulk charge voltage for a flooded lead-acid battery is 14.4V. After a certain time the voltage is brought back to a float voltage of around 13.8v.
The recommended bulk charge voltage for a Narada 12V lead-carbon battery is 13.8V and the float voltage is 13.5V. All these charge voltages are given for a standard temperature of 25 degrees C. As the temperature decreases, the charge voltage can be raised slightly. This is called the temperature compensation factor and is usually around -3 to -5mV per 2V cell. As temperature increases the charge voltage needs to be lowered. The temperature compensation is handled automatically by most modern charging systems, and no change to the usual settings is required for Narada lead-carbon batteries.
If you do not adjust the charge voltages down from those used for flooded lead-acid batteries you will cause damage to lead-carbon batteries. Too high a charge voltage will cause gassing from a sealed battery such as there REXC lead-carbons. As pressure increases inside the battery case due to electrolyte being boiled off by the high voltage it will escape through the pressure relief valve and cannot be replaced. This will cause damage and loss of capacity.
