Choose the SLA or standby battery question that best matches yours
Which SLA battery do I need?
Match the equipment, voltage, application, Ah, size and terminals.
Standby, cyclic or high-rate?
Choose a battery designed for the actual discharge pattern.
How should it be charged?
Float and cyclic charging use different voltage profiles.
How do battery strings work?
Understand series, parallel, matching and whole-string replacement.
My UPS runtime has dropped
Check the UPS model, full string, load, temperature and self-test.
My alarm panel shows a battery fault
Check the charger, battery age, capacity and complete system test.
How should SLA batteries be stored?
Keep them cool, charged and within the recharge-by schedule.
I think the battery is faulty
Charge, test and rule out charger or system causes before claiming.
What do SLA, VRLA and AGM mean?
Sealed Lead-Acid
A common retail term for rechargeable lead-acid batteries with pressure-relief valves and no routine water topping.
Valve Regulated Lead-Acid
The more precise technical term. The battery is normally sealed but includes safety valves that can release gas under abnormal or overcharge conditions.
Absorbent Glass Mat
Most small standby SLA batteries use AGM separators to hold the electrolyte against the plates.
Gelled Electrolyte
A different VRLA technology in which the electrolyte is gelled. AGM and GEL can require different charging profiles.
The battery does not normally need water added, but its charge voltage, temperature, connections, capacity and replacement schedule still require inspection and testing.
Efficient gas recombination occurs during normal operation, but safety valves can vent during excessive charging, heat or failure. Do not place batteries in an unventilated improvised enclosure.
Standby, cyclic and high-rate batteries are designed for different duties
| Battery duty | How it normally operates | Typical applications | Selection priority |
|---|---|---|---|
| Float standby | Remains close to full charge on a controlled float voltage and discharges mainly when mains power fails. | Alarm panels, fire systems, emergency lighting, telecommunications and control equipment. | Approved standby time, design life, float charging, temperature and terminal compatibility. |
| High-rate standby | Remains on float, then supplies high power for a relatively short runtime during an outage. | UPS systems, data cabinets, critical power and high-demand emergency equipment. | Constant-power discharge data, UPS model compatibility, string voltage, current and required runtime. |
| Light cyclic | Experiences occasional discharge and recharge but spends much of its life charged. | Selected backup, portable and intermittent-use equipment where the battery manufacturer approves light cycling. | Cycle limits, depth of discharge, charging time and recovery. |
| Regular cyclic | Is deliberately discharged and recharged frequently as part of normal use. | Mobility, golf, ride-on toys, cleaning machines and traction applications. | Deep-cycle construction, cycle life, charge profile and permitted depth of discharge. |
Standby battery characteristics
- Normally maintained at full charge.
- Limited discharges during service.
- Designed around float charging.
- Availability and design life are key.
- Capacity must meet the required autonomy period.
Cyclic battery characteristics
- Regular planned discharge and recharge.
- Cycle life and depth of discharge are key.
- Often uses a higher cyclic charging voltage.
- Must be recharged promptly after use.
- General standby products may wear rapidly in this duty.
Equal voltage, Ah and dimensions do not prove equal cycle life, discharge power or charger compatibility. Choose a battery range intended for the application.
How to choose the correct SLA or standby battery
Identify the exact equipment
Record the UPS, alarm panel, emergency-lighting unit, control panel or equipment model. Manufacturer replacement data is more reliable than choosing from the old battery alone.
Confirm the battery duty
Decide whether the battery is float standby, high-rate UPS, light cyclic or regular cyclic. This affects the internal design and discharge performance required.
Confirm individual and system voltage
Batteries may be 2V, 4V, 6V or 12V, while the complete system may use several batteries in series to create 24V, 36V, 48V or a much higher DC string.
Match the approved battery technology
Confirm AGM VRLA, GEL, high-rate AGM, flame-retardant case or another specified design. Do not replace VRLA with lithium unless the equipment manufacturer provides an approved conversion.
Match the Ah capacity and rating rate
Capacity may be stated at the 20-hour, 10-hour or another discharge rate. The same nominal Ah can deliver different usable energy at high discharge current.
Check high-rate or runtime performance where required
UPS and critical-power sizing should use the manufacturer's constant-power or constant-current discharge tables at the required runtime, temperature, ageing margin and cutoff voltage.
Measure length, width and total height
Check the enclosure, shelf, retaining bracket and cable clearance. Include terminals in the height where the product specification does so.
Match the terminal type and position
Common small batteries use narrow or wide push-on tabs, while larger batteries use threaded inserts, bolts or front terminals. The connector must fit securely without modification.
Check design life and case specification
Match the required design-life class and any flame-retardant, approval or installation requirement. Design life is conditional and is not a guaranteed service life in every environment.
Check the charger and system settings
Confirm float voltage, cyclic voltage, current limit, temperature compensation and low-voltage cutoff are suitable for the exact battery and complete string.
Replace the complete matched string where required
UPS and series-connected systems commonly require every battery module in the string to be replaced together with matching batteries.
What does a 3–5, 6–9 or 10–12-year design life mean?
Design life is a classification based on defined standby conditions, normally including controlled temperature, correct float voltage and appropriate maintenance. It is not a promise that every installed battery will last that long.
| Example range class | Typical published design-life category | Common use |
|---|---|---|
| Standard commercial | Approximately 3–5 years | Small alarms, control panels, compact UPS and general standby. |
| General purpose | Approximately 6–9 years | Longer-life standby systems where the selected range supports it. |
| Long life | Approximately 10–12 years | Critical emergency lighting, telecoms, UPS and standby systems. |
| Very long life | 12 years or longer | Large critical-power installations and infrastructure. |
Temperature
Heat accelerates grid corrosion, water loss and ageing. The battery temperature can be higher than the room temperature.
Float voltage
Persistent undercharge reduces available capacity, while overcharge causes gas loss, heat and dry-out.
Number and depth of discharges
Standby design life assumes limited discharge events. Frequent or deep cycling consumes life more quickly.
Storage before installation
Long or hot storage without top charging can allow sulphation and capacity loss before the battery enters service.
System condition
Charger faults, poor airflow, loose connections and incorrect cutoffs can shorten battery life.
Required end-of-life capacity
Safety and UPS systems may require planned replacement before total battery failure so the required standby time is retained.
A product described as 10-year or 15-year design life does not automatically deliver that service life in a hot cabinet, at the wrong float voltage or after repeated deep discharge.
How multiple SLA batteries change system voltage and capacity
Series connection
Battery voltages add together while the nominal Ah capacity remains the same as one battery.
Example: two 12V 7Ah batteries = 24V 7Ah.Parallel connection
Voltage remains the same while the nominal Ah capacities add together.
Example: two 12V 7Ah batteries = 12V 14Ah.Series-parallel bank
Multiple matching series strings are connected in parallel to increase both voltage and total capacity.
Requires balanced design, protection and monitoring.Matched batteries are essential
Use the same model, voltage, technology, capacity, age and condition throughout a string or approved bank.
Do not mix AGM, GEL, lithium or different Ah ratings.Understand series and parallel battery arrangements
This calculator shows nominal voltage, Ah and watt-hours only. It does not calculate UPS runtime, fire-alarm compliance or safe cable and fuse sizes.
Enter the battery arrangement above and calculate.
Real autonomy depends on discharge current, cutoff voltage, battery temperature, ageing, charger condition and product discharge curves. High-rate UPS loads can deliver far less runtime than a simple Ah calculation suggests.
Replace the full string where specified
UPS manufacturers commonly require all battery modules in the internal and external string to be replaced together.
Keep new and old batteries separate
Mixing new modules with aged modules causes unequal behaviour and can limit the performance of the complete system.
Check every battery block
A correct total string voltage can hide one weak battery. Compare individual block voltage, condition and test result.
Check links, fuses and connectors
High resistance, loose links or burnt connectors can reduce runtime and create heat even with new batteries.
Internal and external UPS cabinets may require isolation, protective equipment and trained service personnel. Do not open or work on a high-voltage battery string unless authorised and competent to do so.
Why standby and cyclic charge settings are different
Most alarm panels, emergency-lighting units and UPS systems contain built-in charging circuitry. The battery should normally remain connected to the approved equipment charger rather than an improvised external power supply.
Standby float charge
Maintains a standby battery near full charge with a carefully controlled voltage that compensates for self-discharge.
Cyclic charge
Uses a higher charging voltage after a planned discharge, then must reduce to float or stop when charging is complete.
Float voltage too low
The battery remains undercharged, loses usable capacity and can suffer positive-plate deterioration and sulphation.
Float voltage too high
Excess charging can create gas loss, dry-out, heat, swelling and thermal runaway.
Use the exact battery datasheet and charger manual
These are manufacturer examples for a particular battery range, not universal values for every SLA, GEL, high-rate UPS or lithium battery. Temperature compensation and product-specific limits must be followed.
Elevated-voltage modes can damage VRLA batteries and connected alarm, UPS or control electronics. Remove and charge only under the equipment and battery manufacturer's approved procedure.
What to check when UPS runtime falls or the replace-battery warning appears
Identify the exact UPS model
Use the model and serial label, then follow the manufacturer's approved replacement cartridge or battery-string specification.
Check the connected load
Runtime falls as load increases. Compare the present wattage with the UPS rating and original runtime assumptions.
Allow a complete recharge
A recent outage or self-test can leave the string partly discharged. Let the UPS complete its specified recharge period.
Run only the approved self-test
Follow the UPS manual. A self-test under normal load can assess string behaviour more meaningfully than measuring one open-circuit voltage.
Check ambient and internal temperature
UPS batteries often operate warmer than the room. Heat accelerates ageing and reduces service life.
Replace the complete string where required
Do not mix old and new internal or external battery modules in a string unless the UPS manufacturer explicitly permits it.
Reset or record the replacement date
Some UPS models require confirmation that a new battery has been installed so monitoring and future warnings remain accurate.
Do not assume hot-swap capability
Some models support trained-user battery replacement while protecting the load; others require shutdown and isolation. Follow the exact manual.
A UPS may demand high power over only a few minutes. The battery must deliver that power above the UPS cutoff voltage at the required temperature and end-of-life margin. Use the UPS model and manufacturer runtime or battery-sizing data.
Disconnect or shut down only under the UPS manufacturer's safe procedure. Larger systems and high-voltage battery cabinets require trained service personnel.
What to check when a control panel reports a battery fault
Security alarm panel
Check the exact panel model, battery voltage and maximum physical size, then confirm the required standby capacity and charger compatibility.
Fire-alarm system
Battery sizing and testing are safety-critical and must account for the system load, required standby period, alarm period, ageing and applicable maintenance standard.
Emergency lighting
The replacement must support the designed emergency duration. A battery can show normal voltage yet fail the required duration test under load.
Access control and automatic doors
Confirm the standby load, lock or release current, charging profile and safety behaviour during a mains failure.
Do not repeatedly clear or silence the warning without diagnosis.
Record voltage, Ah, part number, terminal type and fitting date.
Use the panel manufacturer procedure and check it against the battery range.
Loose push-on terminals and damaged leads can create a battery fault.
Voltage alone does not confirm that the required standby time remains available.
Do not fit a smaller battery simply because it fits the enclosure.
Confirm the fault clears and the safety system operates as designed.
Panels also use smaller and larger capacities depending on system load, standby requirement and enclosure size. Use the panel manufacturer's battery calculation and approved maximum capacity.
Why a normal voltage reading does not prove standby capacity
Open-circuit voltage
Shows a general state-of-charge indication after the battery has rested, but not the available runtime under load.
Float voltage
Confirms what the equipment charger is applying. A healthy float voltage can appear at the terminals even when battery capacity has deteriorated.
Conductance or internal-resistance test
Useful for trending and identifying weak blocks when the tester is designed for the battery range and application.
Controlled capacity test
Measures whether the battery can support the specified load for the required duration to an approved cutoff voltage.
UPS self-test or runtime test
Evaluates the battery string with the UPS and load, but must be run only according to the UPS manufacturer procedure.
Complete system test
Checks the charger, wiring, fuses, load, battery string, alarms and required standby operation together.
This prevents a charger, connector or equipment fault from being mistaken for a defective battery.
CCA describes engine-starting performance. Alarm, emergency lighting and UPS batteries are normally judged by standby, high-rate or capacity performance.
How to store SLA and VRLA batteries before installation
VRLA batteries self-discharge during storage. Heat shortens the time available before a top charge is required, so stock rotation and the recharge-by date matter.
| Storage temperature | Example shelf-life interval before top charge | Practical guidance |
|---|---|---|
| 0°C to 20°C | Up to around 12 months for the referenced VRLA range | Cool, dry storage gives the longest interval. |
| 21°C to 30°C | Approximately 9 months | Inspect stock and recharge sooner. |
| 31°C to 40°C | Approximately 5 months | Warm storage rapidly shortens shelf life. |
| 41°C to 50°C | Approximately 2.5 months | Avoid this environment wherever possible. |
These are manufacturer examples for a specific industrial VRLA range, not universal limits for every battery. Follow the label, recharge-by date and exact product datasheet.
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Keep batteries cool and dry
Protect them from direct sunlight, heaters, damp and condensation.
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Store upright and protect the terminals
Prevent short circuits from tools, shelves or conductive packaging.
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Rotate stock by manufacture or recharge date
Use the oldest correctly maintained stock first.
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Top charge before extended undercharge develops
Use a charger and procedure approved for the exact battery range.
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Inspect before installation
Reject swollen, leaking, cracked, hot or damaged batteries.
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Charge before commissioning after long storage
Confirm state of charge and capacity before relying on critical standby power.
Why an SLA battery may swell, lose runtime or fail early
Excessive float voltage
Causes overcharge current, gas loss, heat, dry-out and possible swelling.
Float voltage too low
Keeps the battery undercharged and reduces available standby capacity.
High cabinet temperature
Accelerates chemical ageing, corrosion and water loss.
Wrong application duty
A standby battery can wear rapidly when repeatedly deep cycled.
Long storage without top charge
Allows self-discharge and sulphation before installation.
Loose or burnt terminal
Creates resistance, heat and voltage drop and can interrupt charging.
Mixed old and new batteries
Creates uneven behaviour and limits the complete string.
Normal end of service life
Capacity falls with calendar age and use even when the battery has no defect.
Swelling can indicate excessive voltage, heat or thermal runaway. Isolate only under the equipment's safe procedure and arrange replacement and charger diagnosis.
Safe handling and replacement checklist
Shut down or isolate correctly
Follow the equipment manual. Some UPS units support trained hot-swap replacement; others require complete shutdown.
Record the wiring before removal
Photograph polarity, links, fuses, temperature sensors and connectors.
Remove jewellery and use insulated tools
Even small SLA batteries can deliver high short-circuit current.
Check polarity before connection
Reverse polarity can damage the battery, charger and equipment.
Use the correct terminal connector
A loose push-on tab or incorrect bolt can overheat and fail under load.
Secure the battery and cables
Refit trays, brackets, covers, insulation and airflow paths.
Replace every required string module
Use matching batteries and do not mix old and new modules by convenience.
Commission and test the equipment
Confirm charging, fault clearance, self-test, runtime or standby operation and record the replacement date.
Move away and call emergency services if there is an immediate fire risk.
Avoid contact and obtain specialist handling and disposal advice.
Stop charging and investigate the charger and installation.
Stop using the system and inspect for loose connections or excessive current.
Do not open or service it without the required training and protective equipment.
Use a competent engineer to diagnose the charger, load and complete system.
Heat, incorrect float voltage, storage, completed design life, mixed strings, unsuitable duty and repeated deep discharge can all reduce capacity. Charge and test under the correct procedure before arranging a warranty return.
Read the Battery Warranty Guide →SLA, UPS and standby battery FAQs
What does SLA battery mean?
SLA means sealed lead-acid. The more precise term is VRLA, or Valve Regulated Lead-Acid. Most small SLA standby batteries use AGM separators and pressure-relief valves.
Is SLA the same as AGM?
Many small SLA batteries are AGM VRLA batteries, but SLA is a broad retail term. GEL is also a VRLA technology and requires different charging in some applications.
Is a sealed battery completely airtight?
No. A VRLA battery normally recombines gas internally but has pressure-relief valves that can vent during overcharge, heat or abnormal operation. Suitable ventilation is still required.
What is the difference between standby and cyclic batteries?
A standby battery remains on float charge and discharges mainly when mains power fails. A cyclic battery is deliberately discharged and recharged regularly and is built for greater cycle endurance.
Can I use an alarm battery in a ride-on toy or mobility scooter?
Not by assumption. These are regular cyclic applications and can rapidly wear a general standby battery. Use a cyclic battery approved for the equipment.
Why is 12V 7Ah such a common alarm battery?
It provides a practical balance of size and capacity for many small control panels. It is not universal: the correct capacity depends on panel load, standby requirement, charger rating and enclosure size.
Can I replace a 7Ah SLA battery with a 9Ah battery?
Only when the equipment manufacturer approves the capacity, the case and terminals fit, the charger supports it and the required recharge time remains acceptable. Do not assume the larger Ah is automatically suitable.
Can I replace a 7Ah battery with a 7.2Ah or 7.5Ah battery?
It may be an approved equivalent when voltage, application, dimensions, terminals, design life, discharge performance and charger compatibility match. Confirm the equipment specification.
What is the difference between narrow and wide SLA terminals?
Small batteries commonly use different-width push-on tabs. The equipment connector must fit the exact terminal firmly. Do not force a narrow connector onto a wider tab or leave a wide connector loose.
Why does my new SLA battery have different terminals?
Batteries with the same voltage and Ah can be supplied with different tab, bolt or threaded terminals. Check the complete part number and terminal specification before ordering.
Can I charge an SLA battery with a car charger?
Only when the charger explicitly supports the battery's voltage, AGM or GEL technology and small Ah capacity. Automotive repair and recondition modes can be unsuitable.
Can an SLA battery stay on charge continuously?
A standby VRLA battery is designed to remain on the correct temperature-compensated float voltage. It should not remain on an uncontrolled constant-output charger.
Why has my SLA battery swollen?
Common causes include excessive float voltage, high temperature, thermal runaway, charger failure or internal damage. Stop charging and investigate the complete system.
Can a swollen SLA battery be recovered?
No. Do not continue charging or using a swollen battery. Replace it and correct the charger, temperature or system fault that caused the swelling.
Why does an SLA battery show normal voltage but have no runtime?
Open-circuit or float voltage does not prove usable capacity. An aged battery can hold voltage with no load yet collapse during a UPS, alarm or emergency-lighting discharge.
How should an SLA battery be tested?
Inspect it, verify charger voltage, fully charge it and use a conductance, internal-resistance or controlled capacity test suited to the application. Safety systems may require a full duration test.
Can I use a car battery tester on an SLA battery?
A CCA tester is not the correct sole test for a standby battery because the application depends on runtime, power or capacity rather than engine-starting performance.
How long should a UPS battery last?
It depends on the product design life, UPS temperature, number and depth of discharges, float charging, load and maintenance. Many compact UPS VRLA cartridges are commonly replaced in roughly three to five years, but use the exact UPS manufacturer's guidance.
Why has my UPS runtime dropped?
Possible causes include battery ageing, higher connected load, incomplete recharge, high temperature, one weak module or poor connections. Run the approved self-test after a full charge.
Should all UPS batteries be replaced together?
UPS manufacturers commonly require the complete internal and external battery string to be replaced together. Do not mix old and new cartridges or modules unless the UPS manufacturer explicitly permits it.
Can UPS batteries be hot-swapped?
Only on models designed for trained-user hot-swap replacement and only by following the exact manual. Other UPS units must be shut down and isolated.
Why does my alarm panel show a battery fault?
The battery may be aged, discharged, disconnected or unable to support the load. A loose terminal, fuse or charger fault can produce the same warning. Test the complete panel system.
Can I fit a larger alarm battery if it fits the box?
Only when the panel manufacturer permits the capacity and the charger can restore it within the required time. Physical fit alone is not enough.
What does 3–5-year design life mean?
It is a standby design-life classification under defined conditions such as controlled temperature and correct float voltage. It is not a guarantee that every installation will deliver five years of service.
Can I mix old and new SLA batteries in a series string?
This is normally avoided. Different age, capacity and internal condition can cause unequal charging and discharge and limit the whole string.
Can I mix AGM and GEL batteries in one string?
No. They can require different charging profiles and have different electrical characteristics. Use a matched string of the exact approved technology and model.
Can I replace an SLA battery with lithium?
Only where the equipment manufacturer provides an approved lithium battery, BMS and charging solution. Equal voltage and physical size do not make it a safe drop-in replacement.
How should SLA batteries be stored?
Store them charged, upright, cool, dry and protected from short circuit. Follow the recharge-by date and apply an approved top charge sooner when storage temperature is high.
Is a flat SLA battery covered by warranty?
Not simply because it is flat. Incorrect charging, long storage, undercharge, high temperature, completed service life and wrong application must be considered before a manufacturing defect can be confirmed.
How do I recycle an old SLA or UPS battery?
Do not place it in household waste. Use an authorised lead-acid battery recycling route. Local customers can contact Lucas Batteries UK about dropping off suitable used batteries.
Technical sources & review information
Last source check: 29 July 2026
Research basis: Primary manufacturer, regulator and equipment-maker guidance.
Editorial status: Prepared for final Lucas Batteries UK approval before publication.
- GS Yuasa — Cyclic and standby VRLA applications
- GS Yuasa — Correctly charging VRLA batteries
- Schneider Electric — UPS replace-battery warnings and complete strings
- Eaton — UPS installation and whole-set battery replacement
The exact battery datasheet and vehicle or equipment manufacturer's instructions take priority. External source pages and product specifications can change.
Match the equipment, duty and terminals before ordering
Browse our SLA range or send the equipment model, current battery code, voltage, Ah, dimensions, terminal type and number of batteries in the system through our adaptive contact form.