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?


Neither. You need over 13 volts at a minimum to charge a 12 volt battery.
100
milliamps isn't going to do squat, either. Also be aware that solar panels
are
rated under ideal conditions, and you will likely NEVER see anything close
to
the rated output. The panel you describe will actually DRAIN the battery.


All of the small trickle charger solar panels (from decent companys) have a
blocking diode that won't allow the panel to drain the battery. Even a
quality 14V panel will drain a battery at night without a blocking diode.
A 7.2V panel is made to charge a 6V battery, not a 12V battery.

Try a couple tests...
Voc (Open circuit voltage) Test the terminals in FULL Sun. Should be
about 15-18 volts
Vbatt Test the voltage of your battery after it has been charged.
12.4-12.8 V ???
watch the voltage as you connect the solar cell. It should go up a few
10ths of a volt and eventually hit 13-13.5 volts for a small trickle
Do you have a DC ammeter? Do you know how to connect the leads? (it is
usually different than for measuring voltage)
Connect the ammeter in series with the batt and the panel. you should see
some current flow in full sun. Cover the panel. Did it stop? did it go
in reverse? (if it went in reverse... return the panel... no blocking
diode)

I have a small panel (10x14") that I use to keep my underwater scooter
battery fresh. it is the size of a motorcycle battery and although the
panel will NOT charge it, it does keep it healthy in my dock box. it
would not make a dent in my starting batteries. They are too large and
would need a much larger panel to overcome the internal resistance and the
occaisonal bilge pump load.