Welcome to the forum. I agree that it sounds like a battery issue. We’re you able to verify you hooked up the new batteries exactly as the old ones? Hopefully, a few of our 12 volt experts will weigh in.
Your correct the Chassis batteries do the work, both are new both test 100%
The slides operate off the same battery and I have been concerned but no indication.
I still think it's a negative (grounding) problem but can't find the grounding lug on the frame near the chassis batteries. Any ideas? Thanks