What is the make of that box? I'm guessing it is an RVP (RV Products) Battery Control Center (BCC). If so, RV Wizard is very probably right. Most of those have a 50A breaker and it's not hard to exceed that with a weak battery. You can also have problems if you add more or larger batteries, increasing the total amp draw when they get low on charge, or if you upgrade the converter/cahrger to a higher amp model. Does this happen when you've been off-grid for a bit and then plug in or turn genset on to recharge? The inrush of current in that case is sometimes enough to trip that breaker.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC