PowerFilm Rollable Solar Battery Chargers

[S/VSkylark]

Hi all,
I wanted to know if anyone has tried these PowerFilm Rollable Solar Battery Chargers. (http://www.powerfilmsolar.com/rollab...argers/r21.php) I am looking to keep my batteries up while offshore and think this would do. I use very little power, chartplotter, VHF in the day and on top of that mast lights at night, so I would think this would keep up. Here are the specs,
Operating Voltage: 15.4
Operating Current: 1.35 Amps
Dimensions (Un-rolled): 14.5" x 60.75"
The R21 Rollable Solar Charger produces 21 Watts of power at an operating voltage of 15.4 volts

It comes with 15 feet of cable and O ring battery connectors, so it seems to not require a regulator. If thats the case, would I have to disconnect it when connected to shore power and the hard wired charger is doing its thing?
I have 2 batteries in the house bank, so I am assuming if I connect it to one, it will charge the other one as well?
All help is appreciated.
Thanks