“What type of battery should I buy?” is a pretty common question in the motorcycle world. There’s certainly no reason to spend more money and get your battery at the dealership when an aftermarket battery is every bit as good, if not better than (or maybe even identical to) the OEM battery. What’s the difference between conventional, AGM, gel, and lithium, though? Does a more expensive battery actually mean it’s better? Let’s take apart the world of motorcycle batteries and get you the info you need to sort out which type of battery is right for you.

Conventional flooded lead-acid (FLA)

The oldest type of rechargeable battery in the world, an FLA battery is a simple design that consists of electrodes made of sheets of lead or lead-based alloy submerged in a sulfuric acid electrolytic solution.

Advantages

The key advantage of FLA batteries is cost. Since they’ve been around for over 100 years and still are thanks to inexpensive materials and ease of mass production, FLA batteries are very affordable. They’re also an ubiquitous and tried-and-true technology throughout the world.

They also have excellent and consistent high current output for large starter motors.

Despite their reputation, the self-discharge rate of lead acid batteries is actually fairly low, but that comes with some caveats (see disadvantages below).

Disadvantages

Since there is liquid battery acid in an FLA battery, they can only be mounted in an upright position, to prevent leaking of the electrolyte solution. Since they’re not sealed, the acid can also leak out if the battery is subjected to significant turbulence (a bumpy motorcycle ride) or if tipped over. Battery acid can also leak out if the shell of the battery is punctured.

FLA batteries also require a certain amount of maintenance and care to keep them in tip-top shape. Discharge of the battery through use, or through self-discharge from not being used creates a chemical reaction known as sulfation, which is a material that builds up on the electrode plates and reduces the lifespan of the battery over time. Sulfation can be remedied to an extent by keeping the battery charged on a regular basis, and avoiding deep discharge (which causes the sulfation to crystallize, leading to permanent damage). Inevitably, the sulfation build-up will cause the battery to move on to battery heaven.

The water in the electrolyte solution will evaporate over time and needs periodic refilling with deionized or distilled water. Since the acid in the electrolyte is heavier than the water, it can settle over time (stratification), especially when stored in a discharged state. If used in this state, it will cause lower sections of the electrode plates to wear out faster and also make the water susceptible to freezing. Corrosion reduces the lifespan of the battery, and the water freezing reduces cold weather performance and causes damage to the battery.

They’re also pretty darn heavy, because…lead.

Absorbed glass mat (AGM)

AGM batteries are a form of lead-acid battery, but in between the electrode plates is a glass-fiber mat that basically soaks up the electrolyte solution.

Advantages

AGM batteries do not lose substantial amounts of electrolyte to the atmosphere, so they do not require periodic refilling with water for maintenance (their sealed design generally makes this impossible, anyway). As such, they’re often referred to as “maintenance free” batteries.

Since they have a sealed design and the electrolyte is absorbed in the glass fiber, AGM batteries can also be installed in any orientation, will not leak if punctured, and are resistant to shaking (and stirring…sorry, 007).

The glass mat also makes AGM batteries resistant to stratification, preventing uneven wear of the electrode plates, and making them less susceptible to damage in cold weather.

The glass mat that is the electrolyte also serve as separators between the plates in the battery (compared to FLA and gel, where the electrolyte and separators are separate components), adding physical strength and allowing manufacturers to press more electrode plates closer together, thereby increasing energy density.

Since the electrolyte is still in a liquid form within the glass mat (which allows for fast ion movement and current mobility), and AGM batteries typically feature a high acid concentration, AGM batteries have high standby voltage and current output.

They self-discharge slowly, and since they resist sulfation, stratification, and electrolyte loss, can withstand being discharged more completely than FLA batteries without risking damage to the battery.

Disadvantages

The higher acid concentration of AGM batteries is also their downfall. The acid concentration causes the electrodes to wear faster, which reduces the lifespan of AGM batteries. The number of charge/discharge cycles that an AGM battery can withstand is lower than that of other batteries. For instance, the OEM AGM battery in my Kawasaki was toast after two years of daily use. By contrast, I've never actually replaced a conventional FLA battery that I've kept charged and maintained.

AGM batteries are somewhat more complex and costly to produce, and while affordable, do cost more than FLA batteries.

Since they still use lead electrodes, and typically pack more electrode plates into the package, AGM batteries are also pretty heavy.

Gel

Gel batteries add a silica material to the electrolyte solution to turn it from a liquid into a thick semi-fluid gel, just like the stuff you put in your hair in the '80s.

Advantages

The electrolyte is even more resistant to evaporation than AGM, so gel batteries require no maintenance. They are sealed and spill-proof, can be mounted in any orientation, and are unaffected by shaking and bumps.

The gel electrolyte is also very resistant to freezing and boiling, making it great for environments with extreme temperatures.

Gel batteries also self-discharge slowly, and can typically withstand a greater number charge/discharge cycles than FLA and AGM batteries. They can also be discharged more deeply than FLA or AGM batteries without damaging the battery.

Disadvantages

Ex. Pen. Sive. Gel batteries cost even more than their AGM counterparts, and can often carry a price tag that is double that of a conventional FLA battery. Outside of cost, Gel batteries don't really have too many drawbacks.

Lithium

A lithium battery uses the metallic element lithium as the anode in the cell. They’re of course ubiquitous in smartphones, laptops, and other electronics, but much less common in automotive and power sports applications, though their popularity is increasing.

Advantages

The most immediately noticeable advantage is that lithium batteries are mind-bogglingly lightweight. It’s the sort of thing you have to experience to believe. They feel fake and cheap compared to lead batteries, but don’t be deceived. Lithium batteries typically weigh about 1/3 of their various leaded counterparts. Saving weight on a motorcycle is a pretty big deal.

Since there is no liquid to speak of in a lithium battery, they are effectively a sealed design, making them spill-proof and able to be installed in any orientation desired.

Their unique chemistry allows for a phenomenally slow self-discharge rate, so they can be stored long periods of time in between charges. Lithium batteries are also able to be recharged more rapidly than lead cell batteries. Decay of the battery is fairly minimal after many charge/discharge cycles (think about how many times you’re able to recharge the battery on your phone or laptop before it starts failing), leading to a very long overall lifespan.

This unique chemistry also makes them very resistant to cold temperatures, so they perform better and maintain more of their charge and output capacity in cold weather.

They also push out high cranking amps (especially relative to their size/weight) for easy starting.

Disadvantages

Lithium batteries use more exotic materials, expensive manufacturing processes, and are a newer technology. As such, they are as expensive as they are lightweight. You could probably replace conventional FLA batteries, or even AGM or gel batteries in your motorcycle for a decade for the cost of a single lithium battery. It's worth it if you store your bike over the winter and want the peace of mind of low-maintenance, or just don't want the hassle of having to maintain or replace other battery types more frequently.

Lithium batteries also require specifically designed chargers. You can get lithium-specific battery chargers, but if you find yourself charging different types of batteries for your bikes, there are also smart chargers on the market that can charge FLA, AGM, gel, and lithium batteries in one convenient package.