If you don't want complicated circuitry for the charger, you just need to clamp the voltage such that it doesn't exceed around 13.2V for a 12V cell. This is a typical trickle charger setup. You panel is very small compared to the cell, so you should be fine with this.
If you exceed that voltage, you can get to the gassing voltage for a lead acid battery, where capacity is irretrievably lost. This voltage goes down with temperature. It is around 14V at 40C.
If you want to get more efficient charge for your solar power, you can use one of the many solar fed switch mode battery charger chips, like the TI - BQ24650 This also gives you more flexibility for use of LiFePO4, which is starting to replace Lead-Acid. This would probably not make much sense, unless you were wanting a faster charge and using a larger panel. It is capable of 8A charge.