solar panel trickle chargins

I purchased a small flexible solar panel from Silicon Solar Inc. Their web 
site advises that the panel is "perfectly suited as a 12V battery charging

solar solution." Just what I need for trickling the 12 volt starting
battery 
for my dinghy. The solar panel produces 7.2v 100 mA.



A friend, who is an engineer, informed me that I am wasting my time. He
says 
I need 12Volts from the solar panel to charge a 12 volt battery. Thus the 
7.2V will not do it.



Who's right, the manufacturer or my friend?