The unfortunate reality of the batteries in our motorcycles is that we never think of them until that moment we hit the starter button only to hear the telltale “click-click-click” of an almost-dead battery. Lead-acid battery technology has developed over more than a century to the point that, with little or no attention, the battery powering your bike can be 100 percent reliable for many years before needing attention. Here we will look at the current state of lead-acid battery technology, the increasing popularity of lithium-iron as a replacement, and what you need to know about both types of batteries to make sure your own bike starts every time you press that button.
Long ago, motorcycles did not even need batteries to function. Points and a condenser served as the ignition system, the engine was started with a swift kick of a lever, and Bluetooth was what you got after eating blueberries. Now, however, your bike most likely has electric start, an elaborate lighting system, electronic ignition and fuel injection, and any number of electric and electronic accessories and riding aids. Your battery must be able to start the engine, power all those accessories when the engine’s generator can’t keep up (under extended idling, for example), and help protect the delicate electronics from surges and spikes in the system.
Batteries work by converting chemical energy to electrical energy. A single cell consists of a number of plates, or electrodes, submerged in an electrolyte. When charging or discharging, ions (atoms with a positive or negative charge) react with the electrolyte and material on the electrodes to create electrons, which transfer through the completed circuit external to the battery, creating an electrical current. In a conventional lead-acid battery, the electrodes are made from a lead alloy while the electrolyte is sulfuric acid. As the battery discharges, the chemical reaction causes the acid to change to water; charging has the opposite effect, converting the water back to acid. As this happens, the water breaks down into oxygen and hydrogen, and this must be vented to the atmosphere. A single cell generates about two volts of electricity, and six of these are connected in series for a 12-volt motorcycle battery. Hence conventional batteries have six filler caps (through which acid or water can be added) and a vent hose.
Over the years, maintenance-free versions of the lead-acid battery have been developed, which are sealed and do not require venting during normal use (though they do have a safety vent in case overcharging causes an excess of pressure inside the battery). Absorbed glass mat (AGM) technology, used in most motorcycle OEM applications today, uses a very fine fiberglass mat between the electrodes inside the battery, which absorbs the acid to prevent spillage; in addition, any oxygen created when the battery is charged is retained inside the battery, where it can recombine with an active material to form water.
Some aftermarket batteries are of the gel type, in which the electrolyte is mixed into gel form instead of liquid. These batteries are also maintenance free and can be lighter than conventional batteries of similar capacity. The main benefits of AGM and other types of sealed batteries are that they are much less likely to spill acid compared to conventional batteries, and they do not require any occasional top-ups with water.
Aside from voltage and physical size, there are two important specifications for a motorcycle battery. One is the amp-hour (Ah) rating, which indicates the battery’s ability to provide current for an extended period of time. This value is based on 10-hour and 20-hour ratings; for example, an 18 Ah (10HR) battery will provide 1.8 amps of current for 10 hours. The second important specification is cold cranking amps (CCA), which reflects the battery’s ability to provide current and start your bike in low temperatures. A touring bike loaded down with electrical accessories, such as heated grips or aftermarket lights, will require a battery with a high amp-hour rating that can power those devices as you idle along in traffic, whereas starting your high-compression Panigale on a cold spring morning calls for something with a good CCA rating.
Well, not really. If you use your bike regularly, the only maintenance you need worry about is to keep the terminals clean for a good contact. It’s when you don’t ride regularly and let your bike sit for extended periods of time (like over the winter) that your battery will need some attention. Even when your bike’s ignition is in the “off” position, there is still some draw from the electrical system to power accessories, such as a clock or alarm, which can discharge the battery over time. As well, a lead-acid battery can self-discharge when not in use.
As a lead-acid battery discharges, lead sulfate is produced as a by-product and coats the electrode plates. This reduces their effective surface area, reducing the battery’s capacity. Normal charging reverses this process, but leave your battery too long before charging and enough lead sulfate can be produced that charging will not be able to reverse that process—your battery will fail from this condition, called sulfation. A discharged battery is also susceptible to internal corrosion, which can cause the connections inside to break, rendering your battery useless.
Another issue of leaving a conventional battery in a discharged state is that the acid inside turns to water, which in turn can freeze and rupture the case of the battery. And finally, if you let your battery go completely dead—sometimes referred to as deeply discharged—active material falls off the electrode plates and accumulates at the bottom. If enough material collects, it can short the plates, again leaving the battery useless.
For these reasons, lead-acid batteries are best removed or disconnected from the bike and placed on a trickle charger when you expect not to be riding for more than a few weeks. Note that a garden-variety automotive charger can overwhelm your small motorcycle battery; if the battery can’t absorb that high rate of charge, it can overheat (which creates hydrogen gas which in turn may trip the safety valve on a sealed battery or even boil all the electrolyte away). Overcharging can also corrode the electrode plates and terminals. Most “smart” chargers will charge a fully depleted battery quickly and then hold a voltage that will not cause gassing or self-discharge over time. Yuasa recommends 3 amps maximum for charging; in general, divide the amp-hour rating by 10 for the optimum charge rate.
Approximately 1 billion lead-acid batteries are manufactured every year, accounting for 75 percent of the world’s demand for lead. In the powersports industry, GS Yuasa Group, parent company of Yuasa Battery Inc. here in the US, is an OE supplier to many companies and produces more than 50 million powersports batteries worldwide every year. Lead-acid batteries are almost universal for motorcycle OEM use because they are relatively inexpensive to produce, reliable, and able to withstand a lot of abuse with little maintenance. And although the materials are considered hazardous, a lead-acid battery can be almost 100-percent recycled with the polypropylene case and lead used in new batteries and the sulfuric acid safely neutralized.
On the downside, lead-acid batteries are big and heavy for a given capacity, the materials are not good for the environment (if not properly recycled), and they have a limited lifespan. This does not mean that lead-acid batteries will disappear anytime soon, however. “Although the external appearance of Yuasa’s powersports batteries hasn’t changed much over the years,” says Darrell Wilson, Yuasa’s vice president of sales, “we are continuously developing new ways to increase the performance, quality, reliability, and safety of our batteries, both alone and in conjunction with the OEs that we supply.” Wilson points to the company’s YIX20HL battery, which now offers increased cold cranking amps at temperatures as low as minus 20 degrees Fahrenheit for customers with ATVs and snowmobiles in colder climates.
What About Lithium?
Over the past several years, lithium-ion batteries have become more popular in the aftermarket because they are much lighter and smaller than an equivalent lead-acid battery. They are also used in one OEM application: the Ducati Superleggera. In a lithium-ion battery, the positive electrode is made from a lithium-based material, the negative electrode is carbon or graphite, and the electrolyte is an organic solvent with a lithium component. The name lithium-ion refers to the process involved: Lithium ions move back and forth between the electrodes as the battery charges and discharges. There are many different types of lithium-ion batteries, with various amounts of nickel, manganese, cobalt, and iron used in conjunction with lithium to form the positive electrode. Some offer very high energy density but have safety concerns, with thermal runaway (and fire) being an issue.
Lithium-ion batteries are now common in electric and hybrid vehicles, replacing nickel-metal hydride units over the last few years. They are also used in the Victory Empulse and Zero line of electric motorcycles. In the motorcycle aftermarket, lithium-iron batteries are used. Here the batteries get their name from the material used for the positive electrode, a lithium-iron phosphate (LiFePO4 is the molecular formula and sometimes also used to describe the battery type). Lithium-iron batteries offer less energy density than other types of lithium-ion batteries but are more chemically stable and not as susceptible to thermal overrun that can cause a fire.
The biggest advantage of a lithium-iron battery over lead-acid is energy density. In typical applications, the lead-acid battery in your bike can be replaced with a lithium-iron equivalent with as little as one quarter the weight, saving up to several pounds. When we tested a Shorai lithium-iron battery in a Yamaha YZF-R1, the Shorai unit was 5.5 pounds lighter and approximately 25 percent smaller than the stock unit.
Lithium-iron batteries also offer a very long lifespan, more cranking amps, and better resistance to self-discharge, holding a charge for several months. However, lithium-iron batteries will discharge quickly over time if there is any current drain present, as most motorcycles have even when turned off. Full Spectrum recommends disconnecting its batteries if the motorcycle will not be in use for more than 30 days, while Shorai recommends charging the battery every few weeks if you are not riding twice a month.
Lithium-ion batteries require internal electronic circuitry to protect the cells from overcharging or completely discharging, current surges, and extreme temperatures. Most manufacturers of lithium-iron aftermarket batteries require specific chargers be used, as standard chargers may be incapable of correctly reading the voltage of the battery and applying the correct charge and may supply more voltage than the lithium-iron cells can absorb; both conditions can damage the battery. Lithium-iron batteries are also significantly more expensive than lead-acid batteries, and some parts (notably the wires and components in the protection circuitry) can’t be recycled.
While Yuasa does not currently market lithium-ion batteries for OEM or aftermarket use, the company is very active in the technology. “GS Yuasa is a global leader in the development and sale of lithium batteries of various chemistries,” Wilson said. “These lithium batteries are used in many applications, including, but not limited to, electric vehicles, hybrid vehicles, aircraft, satellites, rockets, trains, research submersibles, and military vehicles.” Why not powersports? “Lithium batteries must be controlled by a management unit, and each application has unique requirements regarding how the lithium cells are controlled. Yuasa’s customers trust us to provide batteries that excel in quality, safety, and reliability regardless of the application, so we prioritize these attributes throughout the research and development process. Yuasa is actively developing lithium batteries for powersports applications, but the aforementioned attributes are still considered high priority, so we will not offer any new product until we are confident that it will be the highest quality, safest, and most reliable as possible.”
In 2013, GS Yuasa teamed up with Bosch and Mitsubishi Corporation to form Lithium Energy and Power and pursue the lithium-ion technology. According to a press release issued by Bosch, “GS Yuasa can apply its experience in cell optimization to creating a battery with a higher energy density and increased range. Bosch contributes its expertise in complex battery management and systems integration.”
Late last year, Bosch introduced its own line of lithium-iron aftermarket powersports batteries, the M Li-ion series. “Lithium-ion technology is an important and driving technology for electromobility in general,” Dr. Uwe Thomas, chairman of Bosch’s Automotive Aftermarket business division, said in a press release. “With it, Bosch wants to assume a leading role also in the trade sector in the area of starter batteries.”
According to another press release issued by Bosch, the company “is working on post-lithium-ion batteries, such as those made using lithium-sulfur technology, which promises greater energy density and capacity.” Bosch estimates this technology will be commercially available in approximately 10 years. Yuasa has also had some success in developing a lithium-sulfur battery, which utilizes a sulfur-porous carbon composite for the positive electrode and offers three times the energy density of a conventional lithium-ion battery. Even further into the future, metal-air batteries—using a metal such as lithium, iron, zinc, or aluminum for the anode and oxygen as the cathode—theoretically provide even higher energy density.