Posted by Peter Kennedy on 10/19/2017 to Battery Chargers
AGM batteries are expensive so you want to make sure they get charged in the optimum way. We looked up the specs from a major battery manufacturer, Lifeline, to get their recommendations.
Lifeline have a Detailed Technical Manual for their batteries and chapter 6 covers charging. The charge voltage is based on battery temperature but it uses 25 Deg C, (77 Deg F) as the default temperature and then has compensation tables for higher or lower temperatures.
Lifeline recommend a Bulk and Absorption voltage of 14.3 Volts at standard temperature. For a float voltage they recommend 13.3 Volts at standard temperature. Here is the table showing how these numbers change with temperature:
How does this compare with other battery manufacturers?
All AGM batteries are going to have roughly the same charging parameters but there will undoubtedly be minor differences between manufacturers. I chose Lifeline for the example above because they have a particularly well detailed battery technical manual.
Victron AGM: Bulk and Absorption 14.2 - 14.6 volts (standard service) or 14.6 - 14.9 volts for fast recharge
Float 13.5 - 13.8 volts
Storage 13.2 - 13.5 volts
Trojan AGM: Bulk 14.4 volts
Absorption 14.1 - 14.7 volts
Finish 14.7 volts
Float 13.5 volts
So you see how everyone has some minor variations as to what they recommend
How does this compare to Wet Cell Batteries
Trojan Batteries have a good Users Guide that includes both wet cell and AGM batteries. The recommendations for deep cycle flooded wet cell Trojans are as follows:
Bulk 14.82 volts
Absorption 14.1-14.7 volts
Finish 16.2 volts
Equalize 16.2 volts
Float 13.5 volts