Robert,
I have a similar setup in my IV-P and had planned to replace two of the four batteries every two years, expecting them to last for four years…but I never looked at the expected/advertised life; I was just following a practice used for lead/acid batteries. Two of my batteries are coming up on two years old; the other pair are coming up on four years, and I’d planned to replace them during the condition inspection next month. I’d appreciate your thoughts/experience on this.
Thanks,
Bob