Low voltage startup 38 open

[MC1600]

So I’m going to be curious as to the responses here because I feel I’m close to the same situation with my ‘99 4000 (Cats). My difference is both engines still start fine, but the starting is much peppier if I use the bridge. My first suspicion is batteries which are currently 10yrs old, and I have eyed for replacement soon. But what if that’s not the problem…mmmm…