The easiest way is to note the system voltage, which will be approximately 14 V when the sun is shining on the solar panel and the battery is full (depending on temperature, of course). When the 7 Ah battery is fully charged, the PS100 will limit the current to the battery to milliamps. An ammeter can be inserted in line with one of the solar panel or wall transformer lines to see if the current is very low.
The PS200 and CH200 have a feature that measures the battery current (amperage). If this feature is needed, consider purchasing the PS200.