Battery Basics

A quick guide to lead acid batteries

The term “battery”—meaning, in this case, a device consisting of one or more cells that can produce a direct current by converting chemical energy into electrical energy—became part of our vocabulary when, in 1748, Ben Franklin, noted inventor and revolutionary, used the analogy of an artillery battery to illustrate the collective electrical power of interconnected Leyden jars. Although Leyden jars aren’t batteries as we now think of them, they’re actually a form of capacitor (they’re capable of holding and delivering an electrical charge), so the description was an apt one. Despite Franklin’s clever turn of a phrase, however, it was Italian physicist Alessandro Volta (for whom the “volt” is named) who actually created the world’s first practical battery, in 1800.

By the 1830’s, the gravity cell battery had become a reliable and convenient means of producing electricity. Used mainly to power early telegraph networks the gravity cell type was a forerunner of today’s lead/acid batteries and has much in common with the batteries we're still using.

Because it's permanently sealed after it's filled a maintenance free battery's charge can only be tested with a voltmeter or dedicated testing device. Note the charging instructions on top of the batt
Because it's permanently sealed after it's filled a maintenance free battery's charge can only be tested with a voltmeter or dedicated testing device. Note the charging instructions on top of the battery.Mark Zimmerman

At the Base: Lead Acid
The most common form of motorcycle battery is the lead/acid flooded cell battery, which is a direct descendent of the seminal gravity-style battery. Flooded, or as they're more commonly called, wet cell batteries, are essentially a group of individual cells, each developing between 2.12 and 2.2 direct current volts (depending on their design), that are linked together and housed in a common container. The requisite system voltage is obtained by connecting the cells in a series of three for a six-volt system, and six for the more commonly used 12-volt system.

Each cell consists of groups of lead plates that carry either a positive or a negative charge. The positive ones are commonly made from lead dioxide while the negatively charged ones are typically constructed from spongy lead; however, other lead-based materials can be used, depending on the quality and cost of the battery. The plates are arranged in an alternating, positive-negative-positive pattern, with an insulating material, usually treated paper or fiberglass, placed between them to prevent contact. As you may suspect the surface area of the plates has a direct bearing on the battery’s current capacity; the more plates you have per cell, or the larger the plates, the greater the flow of electricity.

All the positive plates in a cell are linked to each other, as are the negative plates, and in turn, each cell is connected to its neighboring cell in series—positive to negative, negative to positive. Since the series connection provides a cumulative effect, the net result is a battery of the appropriate voltage.

At this point, of course, all you really have is a bunch of connected lead plates, so until we add something to start the required chemical reaction, not much happens.

Some interior and exterior components of a standard battery.
Some interior and exterior components of a standard battery.Courtesy of YUASA

The catalyst is electrolyte, a mixture of distilled water and sulfuric acid. As soon as the electrolyte is added, it reacts with the lead plates and creates an electrical charge, which can be utilized by any electrical load that’s connected to the battery.

Here’s the catch; from the previous description you might think a battery is capable of unlimited output. Obviously, we all know that isn’t true. As the battery discharges, the components undergo chemical changes. The electrolyte degrades into water, and the lead plates become coated with a byproduct of the process called lead sulfate, which hinders efficiency. Eventually the battery goes dead.

During the gravity cell days, dead batteries were rebuilt with new components. It was a nasty, messy job, but when it was done, you had a fresh, fully charged battery. A more convenient solution is to recharge the battery while it’s in use—which is exactly what the charging system does. Whenever an external power source (be it the bike’s charging system or a battery charger) that produces a higher voltage than the battery’s is connected, excess electrons are produced in the battery, which basically restores the battery to its original chemical state. Properly maintained, a charged battery will last for many years, especially if the electrical demands placed on it are moderate.

Nothing's Perfect
Although flooded cell batteries remain popular, they do have several drawbacks. For starters, they're essentially brittle plastic boxes filled with a highly corrosive liquid, and because one of the by-products of a charging wet cell battery is explosive hydrogen gas, the battery needs venting. What comes out of the vent is some very nasty—not to mention corrosive—and explosive stuff.

Because the water evaporates from the cells during the charge-discharge cycles, some periodic topping off of the cells is required, and unfortunately generally neglected, which impacts the battery’s ability to hold a charge. Lastly, wet cell batteries need to be mounted vertically, not only so the plates stay submerged in electrolyte, but to prevent the electrolyte from leaking out through the vents and damaging whatever it contacts. This can present problems when space is at a premium and in a worst case, may cause the bike’s designer to spec a smaller battery than he’d like, simply to fit in the available space.

For those reasons and others, battery manufacturers are constantly working with their customers to build a better mousetrap, and what they’ve come up with is a class of batteries called Valve Regulated Lead Acid Batteries, more commonly known as “maintenance free batteries.”

When kept properly charged, a maintenance free battery can last up to 48 months or more. Use the proper charger to prevent damage from overcharging.
When kept properly charged, a maintenance free battery can last up to 48 months or more. Use the proper charger to prevent damage from overcharging.Mark Zimmerman

Valve Regulated Lead Acid Batteries
The VRLAs, also commonly called sealed batteries, fall into two categories: the Absorbent Glass Mat (AGM) battery and the Gel battery. Although both the AGM and the Gel battery share common characteristics with the flooded cell battery, there are significant differences, and differences between the AGM and Gel types as well.

VRLAs are based on what battery boffins call Gas Recombinant Technology. Exactly how that works isn’t crucial to this discussion, but what is important to know is that whenever a conventional wet cell battery is being charged (be it by the motorcycle’s charging system or a battery charger), the process breaks down water in the cells into its component parts; oxygen and hydrogen. The gasses create pressure inside the battery, so they’re vented to the atmosphere. The result is that water is lost from the cells, leaving only the acid, so we need to top off the battery with distilled water from time to time.

VRLA batteries use lead calcium alloy plates rather than the lead dioxide and spongy lead plates found in conventional batteries, so during the charging phase no hydrogen is produced. Oxygen is still formed, but rather than vent it, the battery chemistry lets it recombine with the active material in the battery to form water, hence you never need to add water. Excess oxygen can be created if the battery is overcharged, so there’s a safety valve/flame arrestor to prevent the battery from rupturing, but you’d have to seriously overcharge the thing to see it pop.

Sealed batteries can be expensive; generally, they’re about double the cost of a conventional battery, but they do offer some significant advantages over the conventional wet cell.

Comparatively high maintenance levels are just one reason why wet cell batteries are being phased out. Note the corroded positive battery terminal and low electrolyte level
Comparatively high maintenance levels are just one reason why wet cell batteries are being phased out. Note the corroded positive battery terminal and low electrolyte level; Somebody hasn't been servicing their battery.Mark Zimmerman

Absorbent Glass Mat Batteries
The most popular form of maintenance-free battery for motorcycle use is the Absorbent Glass Mat Battery, or AGM. The AGM differs from the standard flooded/wet style in that there's no free electrolyte sloshing around in the cells. Instead of a paper (or fiberglass) barrier to separate the lead plates in each cell, the AGM uses a Glass-Fiber mat. Think of the mat as a kind of high-tech, stiff sponge that's constructed of glass fiber and a styrene or acrylic binder, filled with electrolyte and stuffed between the plates. When the battery is initially filled, the electrolyte is absorbed and held in suspension by the mat, the electrolyte staying in contact with the plates through capillary action.

Because the mat is very stiff and strong, it provides the plates with more support so they can be made of a softer, purer lead-calcium alloy, which increases the battery’s efficiency. Because there is no pool of electrolyte that needs to be contained, the battery can produce more current for a given size than the equivalent wet cell battery. It also makes them robust and much better able to resist vibration.

Since the batteries are sealed, maintenance is reduced; in fact, once the battery is filled and the sealing strip is in place, you couldn’t add water if you wanted to, and by the same token, since there is no vent and no acid to leak out, the battery can be mounted in any position. The last characteristic greatly simplifies battery positioning, particularly on bikes where space might be at premium due to the installation of things like EFI computers, ABS plumbing and extra-large air boxes. On that same note, because the plates and separators can be molded into a variety of shapes, AGMs can also be built in a variety of configurations. Optima uses a round cell design that works very well at getting a lot of plates into a very small area.

AGM batteries also hold their charges for extended periods and resist freezing, which makes them very attractive for motorcycle use (many of which are operated only seasonally).

On the downside, AGMs need a charging system capable of pumping out at least 14.0 volts, which may make them unsuitable for use on some older bikes, and they can be damaged if overcharged.

At 11.56 volts this tired wet cell couldn't start an argument.
At 11.56 volts this tired wet cell couldn't start an argument.Mark Zimmerman

The Gist of Gels
AGMs are sometimes confused with "Gel cell" batteries. Understand that AGMs are most certainly not Gel cells; when an AGM is filled, liquid electrolyte is poured into them and if you were to wring out the matt, that's exactly what would come out of them.

On the other hand, true Gel cells (which aren’t often used in motorcycle applications) do not use a liquid electrolyte. They are filled at the factory with a gooey mixture of sulfuric acid, water, and silica—in essence, a highly acidic jelly with the consistency of toothpaste— although in most other respects the Gel battery is constructed along the lines of a wet cell battery.

Gel cell batteries are very good at holding their charge, and they can be run down to very low voltages and recharged without losing much capacity, but in all other respects their performance trails behind both the wet cell and AGM type of batteries. Due to its relatively high internal resistance, the Gel cell just doesn’t pump out as much power as either the wet cell or the AGM, which isn’t much of a problem if you’re using one to provide stand-by power or to run your trolling motor, but might be a real issue if you’re trying to fire up a VTX 1800 on a chilly morning.

Gel batteries are also highly susceptible to overcharging damage. The bottom line here is that they just aren’t as popular as either the wet cell or AGM.

Batteries by the Numbers
All lead acid batteries carry nomenclature that should provide you with some idea of how the battery performs, especially in comparison to a similarly sized and priced battery built by another manufacturer. While a mixture of confusing information may be present, there are only two things you really need to understand: Cold Cranking Amperage and the battery's Amp Hour Rating.

Cold Cranking Amps (CCA) is a measurement of the amperage a battery can deliver at zero degrees Fahrenheit for 30 seconds and not drop below 7.2 volts. This is the most commonly used battery performance standard and indicates how well the battery performs under load at low temperature. Simply put, the higher the CCA, the easier your bike will start, especially during cold weather.

The battery’s Amp Hour Rating describes how long the battery will last at a fixed discharge rate. For small motorcycle batteries, the average is generally calculated over a ten-hour period, at 1/10 of the battery’s amp rating. For example, a 14 Amp-Hour rating means the battery can discharge 1.4 amps for 10 hours. By themselves, the ratings may not mean much, but the rule of thumb is that the higher the CCA and the Amp Hour Rating for a given size battery, the better the battery.

This image depicts a sealed VRLA battery's construction.
This image depicts a sealed VRLA battery's construction.Courtesy of YUASA

Maintain your Charge
Battery manufacturers agree that on average, a motorcycle battery should last 48 months, yet most of us are lucky to get half of that, and in most cases the battery's premature death can be chalked up to a lack of maintenance.

Fortunately, batteries don’t require a whole lot of attention, so take the following steps and there’s a good chance yours will go the distance.

1. Batteries like to be kept clean—a dirty battery can short across the terminals and drain itself in a few hours. Wipe the battery case down occasionally with a damp rag, preferably soaked in a mix of three tablespoons of baking soda and a pint of water—especially if the bike gets ridden under dusty conditions.

Hydrometers measure the specific gravity of a battery's electrolyte.
Hydrometers measure the specific gravity of a battery's electrolyte.Mark Zimmerman

2. Keep the terminals clean, dry, and tight. A light coating of Vaseline or Di-electric grease will protect them from the elements.

3. If your bike uses a wet cell battery, check the electrolyte on a monthly basis and top it off using distilled water whenever the level drops to the add line.

4. If the bike isn't used on a daily basis, keep the battery plugged into a tender. Batteries work best when they're kept as close to fully charged as possible.

Down the Road
As electrical demands grow, so does the need for improved battery technology. In a practical sense, the days of the wet cell battery are numbered. Although they're still a viable device, they're messy, environmentally unfriendly, and not as efficient as the AGM battery, so I expect that over the next few years they'll be phased out, and the AGM will become the standard. In fact, I'd argue that it already has.

As demands for batteries with longer life, more power and even less maintenance increase, the manufacturers will respond in kind. For example, YUASA’s new GYZ20L has a 50 percent lower static discharge rate, provides 11 percent more amperage, and has an 81 percent greater life cycle than the battery it replaces, yet is exactly the same size. Down the road, I expect batteries will develop even more power in a smaller, environmentally cleaner package, and last the life of the motorcycle. How Poor Richard would have described them, I can only imagine.