gilloz says:

Sure you can, as long as the end results of these Solar arrays meets the requirements of the voltage and charging rates of the batteries being charged.
Example: I use a Solar Array that is advertise to keep a trickle charge on your car battery. I use that Array to maintain the charge on 5 C type Ni-Cad batteries (6.25V) to power a security light for my Garden shed in the backyard. Aside from cleaning the Solar Array from dust, I haven’t touched my batteries in over 4 years. Works great.

Added note: I added additional circuitry to bring down the output voltage from 13.5V to 7V.