How To Keep Your Motorcycle Battery Working

Those little boxes of lead and acid are great labor-saving devices, providing you give them a little attention now and then.

Motorcycle lead and acid battery illustration
Give your battery a little bit of attention every now and then to ensure that your bike will start up when you press the starter button.Illustration by Jim Hatch

The growing popularity of cruisers has sent manufacturers scurrying to the archives to revive nostalgic styling features of days gone by—features like floorboards, wide handlebars, and fringed leather saddlebags. The kickstarter, however, seems destined to remain a thing of the past, which is why it’s important to make sure your bike’s battery is always in prime condition. No matter how cool your bike looks, it can’t make up for that sinking feeling you get when you hit the starter button and get a click instead of a rumble.

A typical 12-volt motorcycle battery consists of six individual cells, each of which produces a little over two volts. A cell is essentially a stack of lead plates, and each plate is alternately charged positively and negatively. The lead plates are separated by layers of non-conductive fiberglass or treated paper called the insulator.

Within each cell, the lead plates are interconnected, positive to positive and negative to negative. Each cell is then connected to the next cell in series, or positive to negative. A battery’s output is directly related to the number of lead plates in each cell and their size.

These lead plates grouped into cells aren’t enough to make a battery produce electricity. For that a battery needs electrolyte, sometimes called battery acid because it’s a diluted solution of sulfuric acid in water. A chemical reaction between the lead plates and the sulfuric acid is what produces electricity. This chemical reaction changes the lead to lead sulfate, and at the same time leaves free electrons on the positively charged plates. There they stay until a load is placed on the battery, such as when you turn on the ignition switch. The load causes the electrons to move from the positively charged plates to the negatively charged ones, and that produces electricity.

Battery Multimeter
An inexpensive multimeter, available from Sears, can give a good reading on battery condition, and is also useful for other electrical troubleshooting. You only need a DC voltmeter to test batteries, which is the most basic function of these devices. Unlike a hydrometer, it can be used on sealed batteries and test batteries under light load.Cruiser

Swapping Sulfer
When a battery is producing electricity—which battery techies call the discharge cycle—the electrolyte gives up its sulfur, and some of its oxygen, to the lead plates in the cell. The more of each it gives up, the closer to water it becomes. During the charging phase—when your bike's electrical system is putting voltage back into the battery, or when you put it on an external charger—the sulfur returns to the water, turning it back into electrolyte, and changes the plates from lead sulfate back to lead.

The sulfur in the electrolyte isn’t used up, it just migrates from the electrolyte to the plates and back again. But the charging cycle produces water vapor, which escapes through the battery’s vent tube. Over time, if enough water vapor is lost, the fluid level in the battery goes down. When it does, don’t add more electrolyte. The right amount of sulfur is still present in the remaining electrolyte. Adding more will increase the concentration of sulfuric acid, possibly to the point of harming the battery. All that’s really missing is water, and that’s all you should add—preferably distilled water—which has no minerals to interfere with the battery’s function.

Although water-vapor loss usually occurs over a long period of time, certain conditions can hasten it. For instance, high ambient temperatures and a hot engine can combine to boil out the fluid quickly. A malfunctioning electrical system that overcharges the battery can do the same thing. Aside from the higher concentration of acid harming the battery’s internal components, low fluid levels can also expose the tops of the lead plates to air, which will cause them to oxidize and sulfate.

Even if you keep on top of the fluid level in your battery, it can fall prey to a process called sulfation. In normal battery operation, the lead plates become lead sulfate during the discharge cycle, and are turned back into lead during the charge cycle. Lead sulfate is a crystal, and if it’s allowed to build up on the cell plates, it can destroy a battery. Sulfation usually occurs when a battery is discharged deeply and/or frequently without being recharged. In such cases, the lead sulfate accumulates on the plates, and without a charge cycle to turn them back into lead, the plates eventually crystallize. Sulfation is a white substance that clings to a battery’s cells. The result is a dead battery.

Battery Gauge
It can be hard to distinguish a starter problem from a weak battery. A gauge like this measures current draw and can help pinpoint the problem. Try honking the horn. If the horn sounds weak, it’s probably the battery. A starter problem can be the starter itself, the relay or bad connections.Cruiser

Extending Battery Life
Fortunately, it's fairly easy to prevent sulfation. Make sure your bike's electrical system is in good working order so it replaces the charge lost to starting and running the engine and other electrical accessories. Keep your battery terminals clean and free of corrosion (a bit of silicone or grease can help), and check them now and then to make sure the fasteners haven't vibrated loose. If you don't plan to ride it for an extended period, disconnect the terminals. And most important, charge your battery regularly when it's not in use.

Some riders don’t understand why they need to charge a battery they’re not using. They hop on their bikes after a long lay-off and wonder why the battery is stone dead. The reason is self-discharge, a natural process to which all batteries are subject. Some batteries self-discharge faster than others, and several factors, including the type of battery, determine this. The temperature at which a battery is stored has an effect on the rate of self-discharge. A typical battery discharges at a rate of about one percent per day. Higher ambient temperatures speed the self-discharge rate. A battery stored at 95 degrees, for example, self-discharges twice as fast as one stored at 77 degrees. Temperatures above 130 degrees can kill a battery.

Opposite extremes of temperature can affect a battery too. Pure water freezes at 32 degrees, but electrolyte, which is water and sulfuric acid, won’t freeze until the temperature gets down around minus 75 degrees. The electrolyte in a seriously discharged battery, however, is more water than electrolyte, since the sulfur has migrated to the lead plates. The more discharged the battery, the closer to water the electrolyte becomes, and the higher the temperatures at which it freezes. It’s possible for the electrolyte in a deeply discharged battery to freeze at only a few degrees below the freezing point of water.

There is no truth, by the way, to the old rumor that a battery stored on a concrete floor—or a wooden bench, or a metal shelf, or whatever—will discharge more quickly. The surface on which you store a battery is irrelevant, as long as the battery is stored upright, protected from extremes of temperature, and given a charge on a regular basis.

Start 'Em Young
The right care can prolong the life of a battery, but that care begins before you even install a battery in your bike. You might think that, when you buy a battery and the shop fills it with electrolyte, it's ready to go and you can put it in your bike and ride away. You can, but not if you want it to last. A fresh battery full of electrolyte only has about an 80 percent charge, and will never go higher than that without a pre-installation boost charge. Your bike's electrical system can't handle the job, which is why you should either ask the shop where you bought it to charge it for you, or take it home and put it on a charger before installing it. Follow the battery manufacturer's instructions for charging new batteries, or charge it for three to five hours at a rate equal to 1/10th of its rated capacity. That is, if it's rated at 14 amp-hours, charge it at 1.4 amps.

Battery Hydrometer
For conventional, unsealed lead-acid batteries, a good hydrometer can track battery condition and spot a bad cell. This is the floating-ball type. Each ball has a different weight, and more or fewer float depending on the specific gravity of the battery fluid, which varies as sulfur shifts from plates to fluid and back. Try to measure at 77 degrees F.Cruiser

You'll Get A Charge Out Of This
Even during normal service in a bike with a perfectly functioning electrical system, a battery can lose some of its charge. If your starter cranks a little longer than usual, or your lights are a little dimmer when you first turn on the ignition switch, it's probably time for a charge. Since the charging process gives off hydrogen and oxygen—a combination of gases that can explode if ignited in an enclosed space—make sure the area where you intend to charge the battery is ventilated, and that there are no open flames or sparks nearby.

Loosen the vent caps and make sure the vent tube is unobstructed. Attach the charger leads to the battery, positive to positive and negative to negative, and only then plug in the charger. This reduces the chance of sparks. Charge the battery according to the manufacturer’s instructions. If at any time during the charging process the battery becomes hot to the touch, disconnect the charger and let the battery cool down. Besides damaging the battery, excessive heat build-up can cause it to explode.

Finally, batteries might seem expensive, but they’re dirt cheap compared to eyeballs. Wear safety goggles whenever you work around batteries. Electrolyte is basically weak acid, so clean up any spills right away, and wash it off your hands as soon as you can. If you get some in your eyes, flush them with water for several minutes and call a doctor right away.

There are a number of different types of battery chargers on the market, and they’ll all do the job. Some, however, will do it faster and easier than others. The most common type is the trickle charger, which charges a battery at a fixed rate. The problem with trickle chargers is that they don’t know when the battery reaches full charge. Left unattended, they can boil a battery dry. You need to keep an eye on trickle chargers, and have lots of time in which to do it, because as chargers go, they’re fairly slow.

Taper chargers aren’t much better. They decrease the amount of current going to the battery as the battery’s voltage rises. But you still have to watch them during the charging process to prevent overheating or overcharging, and they’re not much faster than trickle chargers.

The current state-of-the-art tech­nology in home battery chargers is the pulse charger. It monitors the battery’s charge throughout the charging process. Once the battery is fully charged, the pulse charger decreases its output and switches to a stand-by mode, essentially monitoring the battery so you don’t have to. When self-discharge drops the battery’s voltage below a preset level, the pulse charger wakes up and increases its output until the battery is back to full charge. This not only makes pulse chargers the fastest and most convenient on the market, but makes them ideal for long-term battery storage too.

One type of charger you should never use is the high-output type designed to put a quick charge on car batteries. It does so by forcing a high current into the battery very quickly. With their greater capacity and plate volume, car batteries can usually withstand this kind of input, but motorcycle batteries can’t. (However, a car battery can be used to jump-start a motorcycle that has a dead battery.)

Battery pulse-type charger
Pictured is a pulse-type chargers. These keep batteries in peak form without boiling off water, heating the battery or contributing to other problems.Cruiser

Measure Charge
If you're not using a pulse charger that lets you know when your battery is fully charged, you'll need some other way to determine when the battery is ready to go back into service. There are two common ways to do this. The first is with a hydrometer, a device that measures the specific gravity of the electrolyte in each cell, which is indicative of the cell's charge level. There are two types of hydrometers: the floating ball and the calibrated float. The calibrated float is more accurate than the floating ball. Whichever one you use, take your readings at or near 77 degrees. A few degrees either way won't make much difference, but very hot or very cold temperatures can throw off either type of hydrometer.

Voltmeters are a lot easier to use than hydrometers, and are the only way to test the charge on sealed, maintenance-free batteries. Just about any voltmeter capable of reading DC voltage will do the job.

Testing a battery with a hydrometer or a voltmeter is called unloaded testing. You can also load-test a battery one of two ways. The first way involves putting a low load on the battery—by turning on the ignition and lights, for example, while using a voltmeter to check the battery’s voltage. A 12-volt battery should put out at least 11.5 volts DC in this situation (5.75 volts for a 6-volt system). If it doesn’t, it’s time for a recharge.

High-load testing requires a load tester, something any well-equipped motorcycle shop should have. The high-load tester tests a battery’s output under starting loads, which are about the highest it will have to undergo. It’s a far more accurate indicator of a battery’s overall state of health.

The Never-Water Battery
The motorcycle world is catching onto maintenance-free batteries, which have been common in cars for years. Maintenance-free batteries work on the same principles as conventional motorcycle batteries, except that there's no need to replenish the water supply because the battery is sealed.

The separators between the lead plates are made of an absorbent glass mat material that looks like very fine cotton wool. There is no free-flowing electrolyte—it is completely contained within the sponge-like separators. Maintenance-free batteries still give off gases during the charge cycle, but they’re trapped in tiny pockets in the separators and recombine with the electrolyte. Thus, the system is essentially closed, and there’s no need ever to open it. In fact, doing so will ruin a maintenance-free battery.

The name is somewhat misleading because they aren’t completely free from maintenance requirements. Aside from adding water, maintenance-free (or sealed) batteries should be treated the same as conventional batteries, including regular checks and recharges when necessary. These procedures can vary slightly from those used when dealing with conventional batteries, however, so check both the battery manufacturer’s instructions and those that came with your charger for specific details.

All batteries need periodic attention, maybe a little cleaning now and then, and an occasional charge, to keep running at their best, year after year. That’s not too much to ask, either, when you consider the alternative—hitting the starter and hearing that feeble click when you expected a roar. So revel in your bike’s nostalgic styling licks, but remember—take care of your battery and you’ll never miss a kickstarter.