With a 54 watt output you should be able to get around 15-20 amp hours to your batteries on average. Standard 12V house bulbs typically use 1.5 amps/hour or so...and the Davis will use just a few for all night so if this is all you are running and you don't use a LOT of house lights, the panels should be able to keep you going. Given your budgetary concerns...this seems like a good choice.
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