Lithium-battery

Replacing SLA Batteries with Lithium: A Practical Guide for Modern Applications

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Sealed Lead-Acid (SLA) batteries have been used for decades in UPS systems, mobility devices, security equipment, medical carts, and countless industrial applications. They are inexpensive and familiar—but also heavy, slow-charging, maintenance-sensitive, and prone to reduced performance as they age.

Today, as businesses and equipment operators aim for longer runtime, faster charging, and better lifecycle costs, replacing SLA batteries with lithium has become one of the most common and cost-efficient upgrade paths.

This guide explains when you should consider replacing SLA with lithium, what benefits to expect, what compatibility issues to check, and how to upgrade safely with minimal engineering effort.

  1. What Is an SLA Battery and Why Do People Replace It?

SLA stands for Sealed Lead-Acid, a matured battery chemistry built around lead plates, electrolyte, and a sealed enclosure. It falls into the broader VRLA category and includes AGM and Gel variants.

If you need a refresher on how SLA batteries work and how they are structured, you can refer to these deep-dive resources:

SLA batteries are being replaced mainly due to:

  • Shorter lifespan under deep-cycle or high-temperature conditions
  • Heavy weight and large footprint
  • Slow charging times
  • Voltage sag that affects device reliability
  • High total cost of ownership (TCO) despite low upfront cost

All these limitations have led many operators to evaluate lithium upgrades.

  1. Why Replace SLA with Lithium? Key Benefits
  2. 2–5× Longer Lifespan

Lithium iron phosphate (LiFePO₄) batteries typically deliver 2,000–5,000 cycles, compared to 200–400 cycles for SLA.
This dramatically reduces replacement frequency and field maintenance.

  1. Much Higher Usable Energy

An SLA battery can usually discharge only 50% of its rated capacity.
Lithium batteries offer 80–100% usable capacity with stable voltage output.

This means a lithium pack with the same nominal Ah rating can deliver significantly longer runtime.

  1. 50–70% Lower Weight

Lithium batteries are far lighter, improving:

  • Mobility equipment handling
  • Vehicle range and acceleration
  • Installation safety
  • Thermal efficiency
  1. Fast Charging

Lithium supports 1C or higher charging rates, allowing full recharge in 1–3 hours rather than 8–12 hours typical of SLA systems.

  1. Better High-Load Performance

Lithium maintains stable voltage under load, improving reliability in:

  • UPS backup systems
  • Medical carts
  • AGVs/AMRs
  • Security and communications systems
  1. Lower Total Cost of Ownership

Although lithium has a higher upfront price, long-term costs drop due to:

  • Fewer replacements
  • Lower maintenance
  • Reduced energy loss during charging

Most operators break even within 1–2 years.

  1. What Applications Benefit the Most from Replacing SLA with Lithium?
  • UPS and Backup Power

Lithium extends backup duration, cuts charging time between outages, and reduces weight in portable or rack systems.

  • Mobility Devices (Scooters, Wheelchairs, Medical Carts)

Lithium improves daily runtime and reduces downtime from long SLA charging cycles.

  • Industrial & Commercial Equipment

AGVs, floor scrubbers, lifts, and test instruments benefit from higher energy density and more stable voltage.

  • Security, Access Control & Telecom

Lithium eliminates SLA’s issue of accelerated capacity loss under floating and high-temperature environments.

  • Solar & Energy Storage

Lithium provides deeper cycling, longer calendar life, and better charge acceptance for renewable systems.

  1. Considerations Before Replacing SLA with Lithium

Upgrading is typically straightforward, but the following factors must be confirmed:

  1. Voltage Compatibility

Most lithium batteries are direct replacements for:

  • 12V SLA
  • 24V SLA (two 12V in series)
  • 36V / 48V mobility systems

Check:

  • Nominal voltage
  • Full-charge voltage
  • Low-cutoff voltage

LiFePO₄ is usually compatible with SLA system voltage ranges.

  1. Charger Compatibility

Many SLA chargers can charge lithium, as long as:

  • There is no aggressive equalization mode
  • The final voltage matches lithium’s specifications
  • The charger turns off once full

However, a lithium-specific charger ensures optimal life and performance.

  1. Physical Size and Terminal Type

Lithium packs are often built in standard SLA case sizes:

  • Group U1
  • Group 24/27
  • F1/F2 terminals

Still, verify size and mounting constraints before purchasing.

  1. BMS (Battery Management System) Requirements

A lithium battery should include a built-in BMS that handles:

  • Over-charge protection
  • Over-discharge protection
  • Balancing
  • Temperature management

This is crucial for safe SLA-to-lithium replacement.

  1. Current Rating and Peak Load

Check both:

  • Continuous current
  • Peak discharge capability

Applications such as UPS inrush loads or mobility acceleration may require higher peak ratings.

  1. Warranty and Certification

For business and industrial use, verify:

  • UL/CE certifications
  • UN38.3 test reports
  • U.S. warranty terms
  • Cycle-life expectations
  1. Step-by-Step Procedure to Replace SLA with Lithium

Step 1: Review Your Existing SLA Specs

Record the original:

  • Voltage (12V/24V/36V/48V)
  • Capacity (Ah)
  • Dimensions
  • Terminal type
  • Peak load demand

Step 2: Choose a Lithium Replacement with Equivalent or Higher Specs

Ensure appropriate:

  • Voltage
  • Continuous current
  • Peak load rating
  • Operating temperature range

Step 3: Check Charger Compatibility

Replace the charger only if:

  • The SLA charger has equalization mode
  • Output voltage exceeds recommended levels
  • The charging curve does not fully terminate

Step 4: Install the Lithium Battery

Generally plug-and-play.
Ensure correct polarity and secure mounting.

Step 5: Validate Runtime and System Behavior

Confirm:

  • Device starts normally
  • Voltage does not sag under load
  • Runtime meets expectation
  • Charging completes as expected

Step 6: Monitor the First Few Cycles

Lithium performance stabilizes quickly, but early observation ensures compatibility.

  1. Common Mistakes When Replacing SLA with Lithium

Avoid:

  • Matching only Ah instead of usable energy
    (Lithium’s usable Ah is higher even at the same rating.)
  • Ignoring charger compatibility
  • Buying lithium packs without proper BMS
  • Overlooking peak current requirements
  • Selecting packs without proper certifications

These are the most common issues seen from field deployments.

  1. Is Replacing SLA with Lithium Worth It?

In nearly every application involving frequent cycling, high temperature, or long-term TCO considerations, the answer is yes.

Lithium delivers:

  • Longer lifespan
  • Faster charging
  • Stable voltage output
  • Lighter system weight
  • Lower cost over time

SLA remains relevant for low-budget, low-cycle, standby-only environments, but lithium now leads in almost every demanding application.

  1. Recommended Reading

To deepen your understanding of SLA fundamentals and how lithium compares, explore: