Lead Acid Batteries Basics - The Shocking Truth

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Categories: How To, Expert Advice, Repair and Maintenance

Lead Acid Batteries Basics - The Shocking Truth

Motorcycle batteries pretty much fit the theme of "don't leave home without them." More correctly called storage batteries, they literally store electrical power which is generated by the bike's charging system, which in turn is powered by the engine. Virtually all stock gasoline-fueld motorcycles use some form of lead-acid battery and the more you know about them and how they work, the better. So, here goes...

There are three common major lead-acid battery categories: Flooded, Gel, and Asorbed Glass Mat (AGM).

Flooded (aka: Wet Cells) contain liquid electrolyte and are lowest in initial cost. They’re usually not sealed, so the owner can replenish the water in the electrolyte that’s lost while charging the battery. Failure to replace the water can damage or ruin the battery and is one of the most common reasons wet-cell batteries fail. Wet cell batteries are the most fragile type, and the acid can do extensive damage if it leaks out.

Wet Cells require regular, periodic checks of electrolyte levels. In hot weather and following extended high-speed use, they may need to be topped off every few days or weeks. With the bettery positioned level, the height of the electrolyte must at least cover the top of the plates inside, and should be maintained at or near the full marks. Use distilled water to replace the water than has been lost. It's not a good idea to use regular tap water because it contaminates the battery with unwanted minerals, shortening its service life. When removing caps, be careful not to splash the acid-bearing electrolyte, which can destroy clothing, paint and cause severe burns, and even blindness if it gets in the eyes. Wear rubber gloves and eye protection. Wash immediately with water and baking soda mixed together to neutralize the acid. Wet cells can be checked for charge level with a hydrometer. A 100-percent charge yields 1.265 specific gravity, 1.225 is 75-percent charge, 1.190 is 50-percent, 1.155 is 25-percent and 1.120 is discharged.

Checking specific gravity with a hydrometer.

Gel Cells are sealed and use thick electrolyte fluid so they do not spill if they tip over. Both Wet and Gel Cell batteries have lead plates inside but the thicker gel holds up to the rigors of riding quite a bit better and the special vents only allow gas to escape if it is overcharged so there's almost no risk of getting any fuid on you or your bike. The introduction of the Gel battery was the next step in the evolution of powersport battery technology but it has quickly been surpassed by the AGM type. Gel batteries generally require lower charging voltage, so you will need to adjust the charging equipment accordingly. Check the rating on the side of your specific battery, before you hook it up to the charger.

Absorbed Glass Mat (AGM) batteries are the most recent step in lead-acid battery evolution. An AGM uses a fiberglass-type separator to hold the electrolyte in place. AGMs are spill-proof and the most vibration-resistant lead batteries available. The construction of AGMs allows them to be used in rough environments such as off-road racing, where other lead-acid batteries would disintegrate from the abuse of the rough terrain. AGMs typically last a lot longer than wet or gel cells, offsetting their extra cost. AGMs also use almost the same voltage set-points as wet cells and thus can be used as drop-in replacements for them. Both gel and AGM batteries can deliver power at about a 25-percent higher rate than flooded cells. However, since they are also sealed (with small vents), charging has to be controlled or they too can be damaged.

Gel Cells and AGMs require no maintenance as long as the charging system is properly set up. They have no electrolyte to replenish, and never require specific gravity checks. However, keep the mounting brackets securely fastened and clean the terminals on all batteries. Batteries and charging systems can be tested with a DC voltmeter. At rest, a fully charged 12 volt battery should have 12.6 volts, 12.4V indicates approximately 75-percent charge, 12.2V is 50-percent, 12.0V is 25-percent and 11.7V is considered functionally discharged.

Courtesy of Yuasa Batteries

After the engine is started, the voltage should rise gradually to between about 13.6 and 14.4 volts, increasing somewhat as the engine is revved. Another good way to check batteries is with a load tester. With the battery fully charged, the tester draws heavy current. If the battery's voltage drops off quickly it is in weak condition. A good, strong battery's voltage will drop off much more slowly under heavy load.

Batteries are costly, and of course, you want to make sure yours actually needs replacement before you fork-out the cash. Load and charging system tests should first be performed, before deciding to replace the battery. Once you've determined it's is necessary, double check what size battery is needed to physically fit the motorcycle and meet its power requirements. Ths is especially important if you have a used bike that coud have had an incorrect battery installed at some point before you owned it. Batteries typically have their size and type marked on the outside, and it's also listed in most owner's manuals. Besides voltage (typically 12V) batteries come with Amp-hour ratings. Be sure to meet or exceed that requirement. The length of the battery warranty is also a good indicator if its expected lifespan. If you plan on keeping the bike for a long time, get the best battery you can afford.

Note the location of the battery size and charging instructions.

Just because your battery is dead, doesn't always mean it's time to replace it. Batteries can experience two kinds of “dead,” one is permanent and the other is not, if it can be recharged. Many motorcycle batteries are ruined by sulfation, which occurs when the battery is left discharged, and the plates lose their ability to hold a charge. Sometimes, battery chargers with anti-sulfation modes can bring these back to life, but usually it's just temporary. Therefore, the best defenses against dead batteries are to keep the terminals clean, the electrolyte level topped off, and the battery fully charged. Eventually, when your battery really does die or becomes unable to hold a charge, replace it with a new one of sufficient size and capacity for your motorcycle.

We hope this quick guide helps you have a better understanding of what a battery does, how it does it and how to keep yours in good working order. We did not address the new, lightweight prismatic cell, lithium iron phosphate batteries like those made by Shorai, because this piece was intended to be based on the topic of lead-acid bateries only. Feel free to fill in the gaps on anything we might have missed or overlooked and feel free to share any tips that you may have learned over the years too.

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