This is the situation with a conventional AGM (absorbed glass mat) battery. An AGM battery contains a glass mat separator between the plates. The glass mat is saturated with the electrolyte solution and holds the electrolyte in what is, in essence, a contained state, rather than liquid form. This design prevents free-liquid electrolyte from being present, which could spill or overflow.I still use a fillable lead-acid type battery in my 1984 Honda V30 Magna and some of my other older bikes, mainly because they tend to be cheaper. The Magna has spent the long Wisconsin winter months being rotated on and off a Battery Tender in a time-share arrangement with some other motorcycles to keep the batteries in a full state of charge.I don’t recall ever topping up the fluid in this battery since I installed it in April 2017. It is long overdue. Several cells were low on electrolyte—my bad. Despite my inattention, the battery is already over three years old (I use a marker to date each battery when I install it) and still starting the bike immediately. That said, without some maintenance of the electrolyte level, it is unlikely to make it through the season.I have had mixed results with different brands of lead-acid batteries over the years. Some last almost five seasons, while others puke out in less than two. However, most of those short-service incidents occurred before I wised up and invested in Battery Tenders that I now rotate among all my bikes during the winter to keep them all fully charged.Thinking about it, I realized that checking the electrolyte level on a flooded cell battery is something that should be done both fall and spring at a minimum, and more often under high temp or heavy use conditions.Keeping batteries fully charged—particularly in cold, lengthy storage—adds to the service life of any battery, especially the lead-acid type. That’s because a battery stored in a chronically under-charged state will tend to develop sulfation. That shortens battery life and can prevent the battery from being able to recover a fully charged state.Electrolyte is a combination of sulfuric acid and water. The plates in a lead-acid battery should be completely covered with electrolyte. During charging, oxygen and hydrogen gas are released. Those gasses are potentially explosive should a spark be generated, so it’s essential to wear protective gear, including eye protection, when disconnecting or connecting a battery.Tap water has minerals in it that do a battery no good, and water run through water softeners can be particularly harmful. Use distilled water only to protect battery service life. Don’t try to add sulfuric acid. The battery doesn’t lose acid—it is the water that evaporates.Checking the level is relatively easy, as the battery case is usually a translucent material that enables the fluid level in each cell to be checked without removing the battery. If the fluid level is between the top and bottom level marks on the battery case, you’re good to go as long as it’s fully charged. If the level is below the bottom line, it’s time to fill it so the level is back up to the acceptable range.It may or may not be necessary to remove the battery to get at the filler caps. In the case of the Magna, I was able to remove the battery box stay bolt and tip the battery a few degrees to get at the filler plugs.Filling the cells can be a bit of a mess if you’re trying to pour the water into those tiny holes. There tends to be imprecise filling and a mess of spilled water on top of the battery.To prevent that, I use a 60cc piston syringe—usually available at your local pharmacy or medical supply store—and draw up your distilled water out of a bowl. The syringe will have gradients on it to allow precision in how much water you will put in. I tend to draw up 5 to 10cc at a time and check the cell level after each shot to avoid overfilling the cell. That prevents too much dilution of the electrolyte and spillage of excess out of the vent tube, which can cause acid to damage any surfaces it might land on.By dumb luck—which is an important factor in much of the mechanical work I attempt—the tip of the syringe is just about exactly the right diameter for a snug fit in the filler hole on the typical battery, helping to prevent any spillage or blowback. I slowly inject the water into the cell and then have a look to see where the level is until the correct level range is reached.Hot weather and heavy use tend to make a lead-acid battery use up electrolyte more rapidly, so checking more frequently during the riding season is in order.As long as we’re on the subject of hot weather riding and precautions, check out our ideas on that subject.