I Can't think of parasitic load for you. Lights, radio etc go off when you turn off the master switch (You have one and you use it, right?) and no automatic bilge pump. Just an old, tired, battery hat should go to the recycle bin. It looks like raising and lowering the engine when the battery is not charging will continue, so a solar charger might be a nice addition. If you add accessories, add a battery and be sure to use only one battery via the master switch while you're draining one on the sandbar.
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