Replacement of coach batteries

Check that you haven't installed battery cables backwards----reversed polarity

Check that ALL POS cables (large and small) were reinstalled

You hooked something up wrong. You need to go back through everything.
If you hooked them up backwards, you also blew the reverse polarity fuses at your converter. So even if you correct your wiring, things wont work becase of the fuses.

If they are 6 volt batteries, the series jumper could have been hooked positive-to-positive, or negative-to-negative, in which case it's possible no harm was done. If you have an automatic battery interconnect as some Fleetwood models do, do not start the engine until this issue is fixed. A lot of damage could be done when the interconnect kicks in.

As was discussed before, there is a red plastic cap over the positive terminal, remember to remove it before installing cables.