The reason I asked about the Voc is that gov't spec can be be weird voltages like 48V, 72V or higher. Especially if they're designed for communications. That's too much to put into a 12V battery without some kind of step-down. That's the kind of charging that can make hydrogen and explosions. For high voltages you can charge several batteries in series and then draw off of one battery at a time.
If you've got a few bucks, a charge controller is good idea to keep from overcharging your battery, but like Murt says, it's not necessary. A multimeter is really cool too, but you can use a car tail light or dome light to get an idea of voltage. If the light is dim it won't charge a battery. If it goes POP the voltage is too hot. After that you can figure out which wire is positive and negative by very quickly striking sparks across the battery and then switching leads. The smaller sparks are the good ones.
Also, if you've got a ground wire on the panel frame you should ground it. They can build up a massive charge on the frame.