when i bought my unit i challegend that i thought that all four 6volt house batteries should of been changed at the same time instead of two the seller installed stating that two checked out ok. do you think i should bite the bullet and sport for two more new batteries?

Yes.

Definitely second that. You'll get better life and service from the matched set.

In theory, matched batteries are better, but in practical applications, the question is "how closely matched are they?"

In this situation, the age and condition of the first pair of batteries would be the deciding factor. In your instance, we would need to know the testing methods that "checked out OK" on the installed ones.

I have successfully matched batteries up to a year apart when the older ones were identical and well-treated. I used both SG and conductance to check. I recently bought four new ones rather than add a new pair to my existing batteries, even though they tested well. They were over nine years old, so I knew they would not be a good match.

If in doubt, replace all four.