Join Date: Aug 2006
Location: Arlington, VA
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Well, it's a good question. The answer is a definite, "maybe".
Lots of factors in play here.
Type of battery: flooded batteries have a self-discharge rate of 2-10% per week, while AGMs and gelled batteries are more like 1-5% per month. An older flooded battery might lose as much as 1% per day.
The model you're looking at is rated at 2 watts, or approximately 135 milliamps @ 15V. That's a peak rating, when the sun is shining directly on the solar panel.
How much sunlight do you have in your area? Are you in the north? The south?
Let's say you live in the mid-Atlantic region where you might expect 4-5 hours of good sunlight per day. 5 hours x 135 ma = 675 ma or about 2/3 of an amp-hour. If you have, say, a 100AH flooded battery, it might lose as little as .285 AH per day or as much as 1.4 AH per day through self-discharge, in which case your little solar panel would be hard-pressed to keep up even with self-discharge. This doesn't count an additional LOAD on the battery, like if your bilge pump runs.
I'd say the panel is probably undersized for your purpose.
Whatever you do, be sure that the panel you get has a regulator of some sort to avoid OVERCHARGING and damaging your battery.