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Note: this is for deep cycle lead chemistries only.! Lithium chemistries should not be held at full voltage.
In off-grid solar charging scenarios batteries are most often damaged by chronic undercharging. Specifically, not holding the manufacturer's recomended Absorption voltage (Vabs), and not holding that voltage long enough1) for acceptance to drop to endAmps.
Causes of insufficient Absorption:
The Eternal Absorption approach completely forgoes Float stage, forcing the controller to stay in Absorption by setting Vfloat to Vabs. This addresses the controller issues above. It will not address the insolation problem on a given day, but extended Absorption will help reduce damage from previous days of poor harvest.
PWM (and shunt) controllers make more power from panels when battery voltage (Vbatt) is higher.
Eternal Absorption may make timing opportunity loads simpler.