I have a multiplus on our boat that is connected to two 8D AGM that are about 6 years old. Battery bank size 500 Ah.
What I have seen recently is that the multiplus is reporting a low battery alarm in the last 2 out of 3 uses. The two times it has thrown the alarm were with no load introduced that would cause such a sudden drop in voltage level. See attached two charts.
I did a quick test for 30 minutes on the inverter while on the dock. That was with about 140W pulling continuously with one of our fridges periodically kicking in. At the end I put a 1400W additional load on the batteries for 36 seconds and the batteries dropped from 12.5V -> 11.8V
Do folks think that the AGM may just be at the end of their life?