To maybe put it a bit more simply...even if your batteries are discharged to 12.25V (50%) and your 2W panels tries to deliver current at 12.5V...it will only develope less than .2 amps. Given a 5 hour direct sunlight equivilent...this means that over a day..less than one amphour will be stored in your battery. If the bilge pump kicks on, or your radio memory or TV standby function is on you will probably use more than this...hence the lower readings at night. Furthermore...on a 200 amp bank of wet cells..the self discharge rate can easily be in excess of 2 amps per day.
So...briefly...a 2 watt panel is a waste of time and money. Try 20 watts!
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