Guide to Buying SLA Batteries

A sealed lead-acid (SLA) battery is a rechargeable battery that uses lead plates and sulfuric acid, sealed so it never needs water added and can be mounted in more orientations than older flooded designs. SLA batteries power backup systems, medical equipment, alarms, and dozens of other everyday devices. The single most useful fact to know before buying a replacement: match your new battery's voltage, physical dimensions, and terminal type to your old one, and the choice between AGM, gel, and high-discharge designs follows naturally from there. This guide covers the SLA types BatteryClerk Canada carries, how to read sizing and capacity specs, how to charge and install a replacement safely, and how to dispose of the old one responsibly.

Basics of SLA Batteries

"SLA" is a broad category that covers several distinct battery designs, all of which share the same sealed, spill-proof lead-acid chemistry. You'll also see these batteries labeled "sealed lead acid," "valve regulated lead acid," or simply "VRLA" on spec sheets and packaging; all three names describe the same family of sealed, maintenance-free lead-acid batteries. The types BatteryClerk Canada carries are:

AGM (Absorbent Glass Mat): the electrolyte is absorbed into a fiberglass mat rather than sitting as free liquid. AGM batteries handle high current bursts well, resist vibration, and can be mounted in more orientations than older flooded designs, which is why they're the standard choice for most SLA batteries by brand and AJC® SLA batteries sold today.

Gel batteries: the electrolyte is thickened with a silica gelling agent instead of glass mat. Gel batteries are especially resistant to vibration and extreme temperatures, which makes them a strong fit for applications that see repeated, sustained discharges.

VRLA (Valve Regulated Lead Acid): a broader engineering category that includes both AGM and gel designs. VRLA batteries use a one-way pressure relief valve that vents excess gas during charging without letting air (and moisture) in, which is what makes them sealed and maintenance-free in the first place.

High discharge (SLI): short for Starting, Lighting, and Ignition. These batteries are built to deliver a large burst of current for a few seconds, exactly what's needed to crank an engine, which makes them the right choice for powersports equipment like ATVs, UTVs, snowmobiles, and personal watercraft.

A note on deep cycle batteries: deep cycle SLA batteries are a real category, built to deliver a steady, lower-current draw over a long period rather than one big burst, and they're commonly used in marine and RV applications. BatteryClerk Canada does not currently carry deep cycle batteries; if that's what you're shopping for, the types above (AGM, gel, VRLA, and high discharge) cover everything available through BatteryClerk Canada.

Size and Capacity

The size of a replacement SLA battery is important usually because there is limited room where the battery is housed. If the battery is a different size, it may be impossible to fit into the allotted space without some significant reworking. The specs usually include the battery size with length x width x height so make sure to measure and choose one with the same dimensions.

Voltage is a unit of power that is always used with SLA batteries. Typically, you’ll notice 6V or the more common 12V for most of your equipment and in some cases 24V.

The amp rating is also important. The amps of an SLA battery are commonly expressed in terms of the battery's amp-hour (Ah) rating, which is a measure of the battery's capacity. The Ah rating of an SLA battery is a measure of how many amps the battery can deliver over a certain period. For example, a 12V 7Ah battery can deliver 7 amps for one hour, or 1 amp for 7 hours. The higher the Ah rating, the longer the battery can deliver power to a device.

NOTE: Make sure to consider the terminals of the replacement batteries. Again, you want to make sure they match the current battery.

When looking to replace your SLA batteries, finding one with the same voltage and amp rating is recommended to avoid damaging equipment.

SLA vs. AGM: What's the Difference?

This is one of the most common points of confusion for first-time buyers, so it's worth answering directly: AGM batteries are a type of sealed lead-acid (SLA) battery, not a separate category. SLA is the umbrella term for any sealed, maintenance-free lead-acid battery; AGM describes one specific way of building one, using an absorbent glass mat to hold the electrolyte. Every AGM battery is an SLA battery. Not every SLA battery is AGM; some are gel, and some are simply labeled VRLA without specifying which internal design they use.

In practice, this means you don't have to choose between "SLA" and "AGM" as if they were competing options. Here's a concrete example of how this shows up when shopping: a battery labeled simply "12V 7Ah SLA" and one labeled "12V 7Ah AGM" may well be describing the exact same physical battery, since the manufacturer or retailer chose to lead with the general category name in one case and the specific design in the other. When comparing listings, check the detailed spec sheet rather than the headline label; that's where you'll see whether it's actually AGM, gel, or an unspecified general VRLA design. Among the types BatteryClerk Canada actually carries, the more useful comparison is AGM vs. gel vs. general VRLA vs. high discharge, since those are the designs that differ in real, buying-relevant ways:

Size and Capacity

Matching size and capacity is the part of buying a replacement SLA battery that most affects whether it actually fits and performs the way you expect. Start with the physical dimensions: length, width, and height need to match your old battery closely enough to fit the housing, and the terminal type and position need to match so your existing cables reach without strain.

Two electrical specifications matter just as much as the physical fit:

Voltage: most SLA batteries are rated at 6V, 12V, or 24V. Using the wrong voltage isn't a minor mismatch, it will damage the device the battery powers, so this is the first spec to confirm.

Amp-hour (Ah) rating: this describes how much current the battery can deliver over time. For example, a 12V 7Ah battery can deliver 7 amps for one hour, or 1 amp for seven hours; the total energy available is roughly constant, just spread differently depending on the draw. A healthy, fully charged 12V SLA battery typically reads about 12.6 to 12.8 volts at rest (measured a few hours after charging, with no load); a reading meaningfully below that suggests the battery is partially discharged and due for a charge.

Ah ratings vary by application: a small alarm or emergency-light battery might be rated around 1.3Ah to 5Ah, a typical UPS replacement often falls in the 7Ah to 9Ah range, and mobility scooter or wheelchair batteries commonly run 33Ah to 55Ah or higher, since they need to sustain a motor for an extended trip. When in doubt, the Ah rating and voltage printed on your old battery's label are more reliable than guessing based on the device alone.

Brand Quality

Price and brand reputation both matter, but they don't always move together. Before buying, it's worth spending a few minutes reading reviews and comparing specs across brands rather than assuming the most expensive option is automatically the best fit. Look for a manufacturer that publishes clear specifications (voltage, Ah rating, dimensions, and expected cycle life) rather than vague marketing claims, since that transparency is usually a good proxy for a battery that's been properly tested.

A few concrete signals separate a well-built SLA battery from a bargain-bin one: a stated warranty length (most reputable AGM replacements carry at least a one-year warranty), a published cycle-life figure rather than just an amp-hour rating, and clear labeling of the internal design (AGM, gel, or general VRLA) rather than just "sealed lead acid" with no further detail. AGM batteries in particular vary widely in real-world cycle life depending on build quality; a well-made AGM battery under light, shallow discharge cycles can deliver several hundred charge cycles, while a poorly built one can fall well short of its rated capacity within the first year.

Charging

Charging an SLA battery correctly is the single biggest factor in how long it lasts. The charger's voltage needs to match the battery's rated voltage, and the charging current should be sized to the battery's capacity rather than maxed out for speed. A commonly used sizing formula: take the battery's amp-hour rating, multiply by 1.3, then divide by the charger's amp output, to estimate charge time in hours.

It's also worth understanding the difference between two charging modes. Float charging keeps a battery topped off in standby applications, like a UPS or alarm system, where the battery sits fully charged and ready until it's needed. This is different from the charging pattern used after a high-rate discharge application, like a powersports start, where the battery needs a full recharge cycle rather than a light top-off.

One more number worth knowing before you buy: SLA batteries self-discharge on their own even when they're not in use, typically losing somewhere in the range of 3 to 4 percent of their charge per month at room temperature, faster in heat. This is exactly why a battery left in storage for several months without a maintainer can show up dead even though nothing was ever plugged into it.

Installation

Installing a replacement SLA battery is usually straightforward, and the same basic sequence applies across most devices:

1. Confirm the replacement matches the old battery's voltage, Ah rating, dimensions, and terminal type before you start.
2. Disconnect the negative terminal first, then the positive terminal, noting the original cable configuration as you go.
3. Remove the old battery and inspect the housing and cables for corrosion or damage before installing the new one.
4. Place the new battery in the housing in the same orientation as the old one.
5. Reconnect the positive terminal first, then the negative terminal, tightening connections snugly without overtightening.
6. Power on the device and, if you have a multimeter handy, confirm the battery reads within its expected voltage range.

If you're unsure about the specific steps for your device, BatteryClerk's tutorials and guides section walks through the process for many common applications.

Safety

Before handling any SLA battery, inspect it for swelling, cracking, or leaking; a damaged battery should be handled carefully and not charged. Wear gloves and safety glasses when connecting or disconnecting terminals, and remove jewelry and keep loose clothing away from the connection points to avoid getting caught. Avoid setting metal tools across the terminals, since a dropped wrench or screwdriver can short the battery and cause sparking or burns. For a full walkthrough of safe handling, charging, and storage practices, see BatteryClerk's dedicated SLA battery safety guide.

Types and Uses of SLA Batteries

SLA batteries show up across a wide range of equipment, and the right type generally follows the application. Within the types BatteryClerk Canada carries, two broad use cases cover most buyers:

High discharge / SLI batteries are built for powersports applications like motorcycles, ATVs, UTVs, snowmobiles, and personal watercraft, where the battery's job is a short, high-current burst to start the engine.

Standby and backup power applications use general-purpose VRLA or AGM batteries kept on float charge, sitting fully charged and ready for the moment mains power fails. UPS units and alarm systems are the two most common examples, and they rarely need the high burst current of an SLI battery; they mostly need to hold a charge reliably for months or years at a time.

Beyond powersports and backup power, SLA batteries power a long list of everyday equipment BatteryClerk Canada stocks replacements for, including UPS batteries and APC RBC UPS batteries, mobility scooter batteries, wheelchair batteries, emergency light batteries, alarm batteries, lawn mower and tractor batteries, garage door batteries, ride-on toy batteries, generator batteries, electric scooter batteries, two way radio batteries, and vacuum batteries.

Disposal

SLA batteries should never go in household trash. Every SLA battery contains lead and sulfuric acid, both regulated materials, and disposing of one improperly can be both harmful and against provincial regulations. Fortunately, SLA batteries are also among the easiest batteries to recycle responsibly, with recycling rates commonly cited around 99 percent thanks to established lead-acid recycling infrastructure. In Canada, Call2Recycle Canada operates the country's main battery take-back and recycling program, with drop-off locations at many retailers nationwide.

If a battery is swollen, cracked, or leaking, don't drop it in a standard battery recycling bin; contact your municipality's hazardous waste program or a specialized recycler for guidance on handling a damaged battery safely. For a healthy, intact battery, see BatteryClerk's guide to recycling your SLA battery for drop-off options near you.

Frequently Asked Questions

What is a SLA battery?

An SLA (sealed lead-acid) battery is a rechargeable battery that uses lead plates and sulfuric acid, sealed so it never needs water added and can be mounted in more orientations than older flooded lead-acid designs. SLA batteries are used in backup power systems, medical equipment, alarms, powersports vehicles, and many other applications.

What's the difference between SLA and AGM batteries?

AGM batteries are a type of SLA battery, not a separate category. SLA is the umbrella term for any sealed lead-acid battery; AGM refers specifically to a design that holds its electrolyte in an absorbent glass mat. Gel and general VRLA batteries are also types of SLA batteries.

Does BatteryClerk Canada sell deep cycle or marine batteries?

No. BatteryClerk Canada does not currently carry deep cycle, marine, or RV batteries. Our SLA lineup covers AGM, gel, and general VRLA batteries for backup and standby power, plus high discharge (SLI) batteries for powersports applications like ATVs, UTVs, snowmobiles, and personal watercraft.

How long does a SLA battery last?

Most SLA batteries last around 3 to 5 years with proper charging and storage. Actual lifespan depends heavily on how deeply the battery is discharged, how it's charged, and the temperatures it's exposed to; frequent deep discharges and heat both shorten service life.

How do you charge a SLA battery?

Use a charger rated for the battery's voltage and sized to its amp-hour capacity, connecting positive to positive and negative to negative. Standby applications typically use float charging to keep the battery topped off, while batteries used for starting or high-current bursts need a full recharge cycle after each use.

Can you charge a SLA battery with a car charger?

Only carefully, and at a low amperage setting. A high-amp automatic charger built for larger automotive batteries can overheat a small SLA battery, so a charger sized and rated for the specific battery you're charging is the safer choice.

Can you substitute a lithium battery for a SLA battery?

Not directly in most cases. Lithium batteries typically need a lithium-specific charging profile, and voltage curves differ from lead-acid, so simply swapping chemistries without confirming charger and device compatibility can damage the battery or the device. Match voltage, physical size, and terminal type at minimum, and confirm chemistry compatibility with the device manufacturer before substituting.

How do you tell what SLA battery you have?

Check the label on the battery itself for its voltage, amp-hour (Ah) rating, and any model or part number; these are the specifications that matter most for finding an exact replacement. If the label is worn or missing, matching physical dimensions and terminal type to a known compatible battery is the next best approach.

Summary

Finding the right replacement SLA battery comes down to matching a handful of specifications, voltage, amp-hour capacity, physical dimensions, and terminal type, to what your device already uses. From there, the choice between AGM, gel, and high-discharge designs follows naturally from how the application actually uses the battery, and remembering that AGM is simply one type of SLA battery, not a competing category, clears up most of the remaining confusion. Charge it correctly, store it on a maintainer if it sits unused, and recycle it responsibly through Call2Recycle Canada at the end of its service life.

BatteryClerk Canada carries affordable, quality-tested alternatives to original manufacturer batteries across all of these types, with 1-2 day shipping to most of Canada. Browse SLA batteries by brand or AJC® SLA batteries to find your exact replacement.