Casual Tenders cannot repair their PFs, as others have pointed out. They do have reload facilities though.
The Lyran capitol ships ARE true tenders. If you use them either without PFs or before PFs are available you replace the repair boxes with cargo and delete the mech links. The repair boxes would be of no use without the PFs. They cannot be used to repair the systems on the main ship.
As a side note, because I know that you are also interested in Andros, The Andromedan motherships are an exception to the rule that doesn't allow self repair by accessing the repair boxes. It is, IIRC, twice as expensive to use the repair boxes for self repair though than to use the systems on the SatShips. Which is their true intent.