Technical FAQ on Sealed Lead Acid (SLA / VRLA) batteries for UPS systems and other backup applications. Covers battery basics, voltage and capacity matching, shelf life, swelling, and smart vs dumb battery monitoring. For application-specific UPS questions see our UPS FAQ; for replacement-decision questions see our UPS Battery FAQ; or browse compatible cells in our all-UPS replacement battery hub.
What is a Sealed Lead Acid (SLA) Battery?
A Sealed Lead Acid (SLA) battery, also known as a Valve Regulated Lead Acid (VRLA) battery, is designed to be maintenance-free, leak-proof, and position-insensitive. It features a safety vent that releases excess gas if internal pressure becomes too high. Two common SLA chemistries are AGM (Absorbed Glass Mat) and Gel — most UPS replacement batteries are AGM.
SLA batteries are widely used across various applications, including:
- UPS systems (the primary use — see our all-UPS replacement battery hub)
- Home alarm and backup systems
- Generators
- Flashlights and spotlights
- Exercise equipment
- Motorcycles and ATVs
- Toys and more
These versatile batteries are valued for their reliability and durability in both consumer and industrial settings.
What are Volts and Amp-Hours (e.g., 12V – 20Ah)?
Every battery is rated based on two key factors: voltage (V) and amp-hours (Ah).
- Voltage (V): This measures the battery's electrical potential. Common battery types include 2V, 4V, 6V, 8V, 12V, and 24V.
- Amp-Hours (Ah): This indicates how much energy the battery can store, essentially reflecting how long the battery can supply a specific amount of current before it needs recharging.
Together, these ratings help determine the battery's capacity and suitability for various applications. To translate Ah into expected UPS runtime at your real load, use our UPS runtime calculator.
Does My Replacement Battery's Capacity (Ah) Need to Match the Original? How Do I Choose?
Not always. If the battery's physical dimensions allow it, you can upgrade to a higher capacity (Ah) battery for longer runtime. For example, a device using a 12V 7.2Ah battery can be upgraded to a 12V 9Ah battery without issue, as long as it fits the compartment.
However, voltage (V) must match exactly. In the example above, the replacement battery must be 12V, even if the amp-hour rating changes. Using a different voltage could damage your device.
For UPS-specific replacement, also match the OEM cartridge code when possible — APC RBC7, RBC55, RBC44; Eaton 744-A2025, 744-A2026; Vertiv/Liebert GXT cells; Tripp Lite RBC. Browse compatible cells in our all-UPS replacement battery hub.
How Long Do SLA Batteries Typically Last?
Most Sealed Lead Acid (SLA) batteries have a lifespan of three to five years, depending on factors such as the application, charging method, and operating temperature. They typically last for 300 to 500 cycles.
To maximize battery life, always charge the battery before storage. Storing an SLA battery in a partially charged or discharged state can cause permanent damage. Operating temperature also matters — every 8°C above 25°C halves SLA life (Arrhenius rule of thumb), so cool, ventilated UPS placement is critical for fleet ROI.
For scheduled changeouts in business environments, see our UPS battery replacement service.
What is the Shelf Life of a Sealed Lead Acid (SLA) Battery?
SLA batteries naturally discharge over time, typically self-discharging at around 3% per month. If not periodically recharged, they may never regain full capacity. It is recommended to check and charge every three months and never store for more than six months without recharging. Store SLA batteries in a cool, dry place. Under proper storage conditions (around 25°C), they can last 6 months to 1 year on the shelf.
What is "Memory Effect"?
SLA batteries do not experience memory effect. Memory effect, also known as "lazy battery effect," occurs in some rechargeable batteries — primarily older NiCd batteries — that lose capacity when recharged without being fully discharged first.
For SLA batteries:
- Never fully discharge them.
- Always recharge after use to extend battery life. Frequent deep discharges reduce longevity, while maintaining a full charge helps them last longer.
Lithium-ion UPS batteries (e.g., Eaton 9PX-Li) have completely different chemistry and don't suffer memory effect either, but they have their own deep-discharge protection circuitry that's worth respecting.
My Sealed Lead Acid Battery is Bloated or Swollen. What Should I Do?
If an SLA battery is swollen or bloated, immediately remove it from the device. Swelling typically results from overcharging, which causes overheating. This can lead to a dangerous condition known as thermal runaway, where the battery heats up and accepts more current, accelerating the heat cycle.
Swollen batteries are not safe for use and must be recycled at a local battery recycling facility. Lead-acid is regulated under provincial Hazardous Waste rules in Canada — don't put SLA batteries in regular trash. Call2Recycle Canada operates a free drop-off network nationally. Replace the damaged battery as soon as possible — our UPS battery replacement service handles disposal of old cells as part of the install.
How Long Will My Battery Run?
Battery runtime depends on the power demands of the equipment, as well as the battery's capacity and usage conditions. Every application is different, so it's best to contact your device's manufacturer for an accurate estimate based on the specified battery.
For UPS-specific runtime estimates at your real load, run the numbers through our UPS runtime calculator. As a rule of thumb, a 1500VA UPS with a standard 12V 9Ah battery delivers 5–15 minutes at full load and 30–120 minutes at light loads.
What are "Smart" and "Dumb" Batteries?
- Smart Batteries: Contain internal circuit boards that communicate with the device or UPS to monitor performance, output voltage, and temperature. Most modern UPS battery cartridges (APC RBC, Eaton 744-series) include smart-battery features so the host UPS can run accurate self-tests and predict end-of-life.
- Dumb Batteries: Do not have this monitoring capability and simply provide power without additional feedback. Replacement "compatible" cells are sometimes dumb — they work electrically but the host UPS may need a manual calibration cycle after install.
Are the Sealed Lead Acid Batteries You Sell Rechargeable?
Yes, all SLA batteries sold are rechargeable. They're designed for repeated charge-discharge cycles in UPS systems and other backup applications, typically delivering 300–500 cycles over a 3–5 year service life.
My System Uses 4 Sealed Lead Acid Batteries. Can I Replace Just One?
No, it's recommended to replace all four batteries at the same time. Replacing just one will lead to premature failure of the new battery because the older batteries can damage it. Even if the other batteries aren't completely dead, they are likely degraded and will soon fail as well. The new cell will be charged-discharged at the rate of the weakest old cell in the string. To maximize the life of your system, replace all the batteries with new ones at once.
Need Help With Your UPS Battery? Contact Us Today
For expert advice on choosing, installing, or maintaining your UPS battery, get in touch with UPSPLUSBATTERY. We service APC, Eaton, Tripp Lite, Vertiv, Liebert, Powerware, and Cyber Power batteries across Canada through our parent company GDF Technologies.