Since you stipulated 5 batteries I assume they are 12 volts each hence each will have 6 cells for a total of 30 cells. A liter of water is about 33 ounces or slightly over a quart indicating that each cell is requiring slightly more than an ounce of water every two months. Frankly, considerig the environmental conditions--Mexico/Summer--that does not seem like an unusual amout of water at all. Depending upon how long you will be gone, however, it might have been wiser to simply turn everything off, including the master switch to the batteries, which would loose only roughly 1-1/2% to 2% of their charge per month which could be restored with only a few hours of charging once a month.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."