Is the SolaX X1-FIT W X1-FIT-3.7-W compatible with the SolaX No?

Yes — listed by the manufacturer.

Offered as a parallel-box option alongside this inverter's battery ecosystem.

Minute Solar records SolaX X1-FIT W X1-FIT-3.7-W with SolaX No as compatible (A — Automatic). Derived from recorded specifications or compatibility groups; no manufacturer approval is recorded.

▦Manufacturer's compatibility listListed together in the manufacturer's published pairing data. A cited document reference is being added as datasheets are processed.