Simplistically, a solar panel is like a current source; if you connect a small panel directly to a battery, the terminal voltage of the battery will be determined by the state-of-charge of the battery. As the small current from the panel flows into the battery, the battery voltage will slowly rise.
To the extent that the daily Ah output from the panel exceeds the self-discharge and load discharge current of the battery, the battery will eventually reach full charge, as evidenced by the SLA battery voltage creeping up above 2.35V per cell. That is point at which you either have to disconnect the panel, or put a regulator set to 2.25V per cell between the panel and the battery. If the average external Ah load (plus the battery's self discharge rate) is equal to or greater than the Ah output of the panel, then the battery will just hold its own, or slowly loose charge, in which case the battery voltage will slowly get lower, and no regulator is needed.