It's hard enough to find time to enjoy your boat in between all the different things going on; we're always so busy! It's even harder to find the spare time to do monthly checks on your boat. There are always things that need to be maintained and checked on a boat - it is never a good idea to tuck your boat into its berth and forget about it. Many systems onboard need to be checked at least once a month, if not more. Pumps are a prime example of components onboard that should be used (meaning turned on or rotated) regularly to prevent them from seizing or letting the impellers dry out.
A lot of people are now replacing their old flooded cell batteries for AGMs, which are maintenance free, but only to a certain point. Sure, the battery itself doesn't need to be checked for water depletion, but the connections on top do. If you see a buildup of chemical residue on your terminals/connections, then you should clean this area right away. With your battery switches turned OFF, pour hot water over the terminal/connections; this should wash away the unwanted residue. For a 100% improved connection, disconnect the affected cable connection and file the lug clean till you see it shine copper. This will help with the passing of current through your connections and cables to give you the best power supply.
If your batteries are flooded cell batteries, then the water level is something that should be maintained. The water should sit right on the bottom of the lip where the cap goes on. To be clear, I don't mean the very top of the cell, but the bottom of the plastic tube that runs down away from the opening of the battery cell (about one inch from the top). Keep in mind that even when you aren't using your boat and your batteries are just sitting on a float charge, there is still a chemical reaction taking place in the battery that causes it to vent gas. Over time, this reaction will deplete the fluid in your battery and will need to be replenished.
Letting your batteries run dry is a terrible thing, and can cost you in more ways than one. Also, keep your batteries free of any dust or water that may find its way to sit on top of your battery. A clean battery is a happy battery, that's for sure!
A quick safety note: Always wear the right safety gloves and eye goggles when working on batteries, and make sure you have the battery switch and chargers turned OFF. Keep water nearby in case any acid spills onto you or the items around you.