Solar controller selection for existing pannels

All I could afford wrote:

In full sun, with my multimeter on the terminals coming from the pannels I am showing about 18 volts, as expected. However, I am showing the exact same voltage on the terminals going to the battery compartment.

Is this attached to a battery?

attach to a battery and remeasure and re-post results.

New, those panels should measure 21v not connected to a battery, relatively cool, 25C.
connected to a battery while charging, you should measure batt V.