My WFCO 8725P stays connected 24/7 when in storage. It is charging and maintaining a pair of gel batteries that sell for $275 each. No problems after several years.
You can replace just the charging portion with some other brand converter and simply disable the one in the WFCO power center. It won't solve your issue though. It sounds as if you are overloading one of the branch circuits.
There is no way your converter could utilize a 15 amp fuse in the charging circuit since it puts out 35 amps. That is why it has 40 amp fuses in the charging circuit.