In order,
Frank, if your solar system is undersized, you are right, it will not keep up with the internal resistance of the battery.
Geha, If your battery is a single deep cycle battery, what I posted above will work for you as well.
Allen, If the batteries are used in parallel, one Brat can supply enough amps to charge them both. I would recommend 120-200 watts worth of solar panels for optimum service. Cheep chargers will not have the correct diode sizing and current could flow backwards from the battery through the controller to the panels, heating them up some, and draining your batteries. Go With Quality.
Frank rev 2, Solar is not risky, improper solar is risky. Sized appropriately, solar is a good choice for remote needs.
Mark, you are using a thin film panel and it can loose as much as 30% of its capability in six to nine months. At five watts, you are not putting enough energy into a deep cycle battery to keep up with its internal resistance. You really need poly or mono crystal panels and 80-100 watts per battery if you want to rely on solar for any recharge (50 watts worth of solar would be the minimum I would recommend). It is all about the math.
Allen rev2, I got your back it is doable and mounting it on the dock would make it very convenient. The only thing we will have to make sure of is that the panel is "turned off" before disconnecting the batteries so as to not hurt the Brat.
