Wildbill;
Good to see those NiCds are working for you.
If you're using a 12vdc PV then try using a simple diode & cap DC-DC voltage doubler setup.
The PV is small enough that you shouldn't have any over charging problems.
The doubled voltage will be fine I've seen these take 22vdc on a deep cycle and still be just fine, your current is still low enough to keep them from getting hot and the diodes should give you enough voltage drop to come down to a useable voltage.
I can't make use of this, as I drain the NiCds too far down and it'd take mine a week to just charge on set let alone 20.
What was your up time on that pack?
Bruce S