"Houston, we have a problem..."
For many organisations, a two-way radio system is far more than just a convenient means of communication. It is a critical operational tool that supports security teams, facilities management, estates personnel, maintenance engineers, event staff, and emergency response procedures.
Yet one aspect of radio system design is frequently overlooked until it is too late: what happens if the mains power fails?
A power outage that disables a repeater can instantly take an entire radio network out of service, precisely when reliable communications are needed most.
A radio repeater backup power system keeps your repeater running during a mains failure. The main options are a standard AC UPS, a dedicated DC battery connected directly to the repeater, or a fully DC-powered infrastructure.
This article explains why backup power should be considered for every repeater installation, the options available, and how to determine the most appropriate solution for your organisation.
Why Do Power Outages Occur?
Although many people think of power cuts as rare events, interruptions to the electricity supply can occur for many reasons, including:
- Utility network faults
- Severe weather
- Localised cable damage
- Planned electrical maintenance
- Building electrical faults
- Distribution board trips
- Generator failures
- Accidental isolation during building works
Some outages last only a few seconds or minutes, while others may continue for several hours.
Unfortunately, your need for reliable communications does not stop simply because the electricity has.
What Happens When a Repeater Loses Power?
A repeater provides the communications backbone that allows handheld and mobile radios to communicate reliably across buildings, campuses, industrial sites and multiple locations.
If the repeater loses power, the consequences can be significant.
Depending on the system design, users may experience:
- Complete loss of radio communications.
- Loss of communications between different buildings or areas of the site.
- Failure of linked or networked radio systems.
- Inability for users to reach one another across the intended coverage area.
- Loss of communications during emergency or evacuation procedures.
Although many radios can be programmed with a direct (simplex) talkaround channel, this typically provides only limited local coverage and cannot replace the wide-area coverage provided by a repeater.
For many organisations, a functioning repeater is essential to maintaining effective communications.
What Does It Cost When a Radio Repeater Goes Down?
The consequences of a repeater outage extend well beyond inconvenience.
Potential impacts include:
- Delayed evacuation procedures.
- Reduced coordination between response teams.
- Increased security risks.
- Disrupted facilities management.
- Business interruption.
- Reduced productivity.
- Increased operational costs.
- Reduced staff safety.
Many organisations only discover how dependent they are on their repeater after experiencing their first significant power outage.
If two-way radios form part of your emergency response or business continuity procedures, ensuring the repeater remains operational during a mains failure should be an important part of your resilience planning.
How Long Should Backup Power Last?
There is no single correct answer.
The appropriate backup period depends entirely on how the radio system is used and the operational risks associated with losing communications.
Typical requirements include:
- 15–30 minutes – Protection against brief interruptions and power fluctuations.
- 1–2 hours – Suitable for many commercial buildings and shorter utility outages.
- 4 hours – Allows communications to remain available throughout most operational incidents and building evacuations.
- 8–10 hours or longer – Appropriate where extended resilience is required or prolonged outages are considered credible.
Longer backup times naturally require larger battery capacity and should be balanced against operational need and cost.
Choosing the Right Backup Solution
Several approaches are available depending on the level of resilience required.
Option 1 – Standard AC UPS
A conventional UPS (Uninterruptible Power Supply) is often the simplest solution.
The repeater is powered from the UPS, which automatically supplies battery power if the mains fails.
Advantages
- Quick to install.
- Minimal changes to existing equipment.
- Ideal for short-duration outages.
- Readily available.
- Protects against brief power interruptions and voltage disturbances.
Considerations
- Larger battery autonomy can become expensive.
- UPS batteries require periodic replacement.
- Energy is continually converted between AC and DC, reducing efficiency.
- Very long runtimes may require external battery packs.
For many commercial installations, a conventional UPS provides an effective and economical solution.
Option 2 – Dedicated DC Battery Backup
Many professional radio repeaters, including models such as the Motorola SLR5500, include a dedicated DC battery connection.
This allows a standby battery to be connected directly to the repeater.
Under normal operation:
- The repeater operates from its normal power supply.
- The battery is maintained in a charged condition.
- Should the mains supply fail, the repeater automatically continues operating from battery power with no operator intervention.
Advantages
- Higher efficiency.
- Fewer power conversion losses.
- Excellent reliability.
- Ideal for extended backup periods.
- Simpler architecture than large AC UPS systems.
This approach is widely used within professional radio infrastructure and telecommunications environments.
Option 3 – Fully DC-Powered Infrastructure
Many professional communications installations take resilience one step further by powering the repeater from a dedicated DC power system rather than directly from the mains.
In this arrangement, the repeater operates continuously from a regulated DC power supply, with one or more standby batteries permanently connected to the same DC bus.
During normal operation:
- The DC power supply powers the repeater.
- The batteries are maintained on float charge.
- Should the mains supply fail, the batteries immediately continue supplying the repeater with no interruption to service.
Unlike a conventional UPS, there is no inverter stage continually converting between AC and DC, making the system simpler, more efficient and particularly well suited to communications equipment.
For applications requiring an even higher level of resilience, the DC power system can itself be designed with redundancy. Dual hot-swappable DC power supply modules can be installed in parallel so that if one power supply develops a fault or requires replacement, the second continues to support the repeater without interruption.
Combined with a standby battery bank, this arrangement provides protection against both mains power failures and individual power supply failures, significantly reducing the risk of an unexpected loss of communications.
This architecture is widely used throughout the telecommunications industry and is considered best practice wherever continuous availability of communications is business-critical.
How Is Battery Capacity Selected?
Selecting the correct battery involves considerably more than multiplying current by time.
A properly engineered solution considers:
- The manufacturer's published equipment current consumption.
- Expected transmit duty cycle.
- Increased radio traffic during emergencies.
- Battery ageing throughout its service life.
- Ambient temperature.
- Reserve operating capacity.
- Manufacturing tolerances.
- Required reliability over many years of operation.
Providing adequate design headroom helps ensure the system continues to deliver the intended backup duration throughout the battery's operational life, rather than only when the battery is brand new.
Questions to Ask Before Choosing a Backup Solution
Every installation is different. Before selecting a UPS or battery system, consider the following questions.
How long do power outages typically last?
Historical outage data often provides a useful starting point.
What happens if radio communications are lost?
Is it simply inconvenient, or could it impact safety, security or business continuity?
How long do communications actually need to remain operational?
The answer may be very different from simply selecting the longest possible runtime.
What equipment requires backup power?
It may not only be the repeater.
Also consider:
- Network switches.
- Routers.
- Internet connections.
- IP linking equipment.
- Microwave links.
- Dispatch consoles.
- Control equipment.
Powering only the repeater may not maintain the complete radio system if supporting infrastructure also loses power.
Is there already a standby generator?
If generator-backed supplies are available, the battery system may only need to bridge the period until generator power becomes available.
Which Backup Power Option Is Right for You?
The table below summarises the three main approaches covered in this guide. Costs are indicative and will vary depending on supplier, battery capacity and whether professional installation is included.
Standard AC UPS | Dedicated DC Battery Backup | Fully DC Infrastructure | |
How it works | The repeater runs from the UPS on mains power. If mains fails, the UPS switches to its internal battery automatically, with no interruption to the repeater. | A standby battery is wired directly to the repeater's DC input. The repeater charges the battery during normal operation and draws from it when mains power is lost. | The repeater is permanently powered from a managed DC power system (rectifier + battery bank) rather than mains AC. Mains failure causes no change in operation. |
Switchover time | Typically under 10-20 milliseconds — effectively seamless | Zero switchover — battery is always connected | Zero switchover — no mains dependency at all |
Typical equipment cost | £ - £££ | ££ - £££ | £££ - £££££ |
Installation complexity | Low | Medium | High |
Typical backup duration | 2–8 hours | 4–24+ hours | 24–72+ hours |
Battery chemistry | Sealed lead-acid (internal, typically non-replaceable on smaller units) | Sealed lead-acid (AGM) or lithium (LiFePO4) — user-specified | AGM, VRLA or lithium — specified at design stage |
Maintenance requirements | Low — battery health monitoring via software; replace battery every 3–5 years | Medium — battery voltage checks, terminal inspection, periodic load testing | Medium–high — regular inspection, load testing, rectifier servicing |
Suitable for | Most commercial and light industrial installations; smaller sites; budget-conscious deployments | Repeaters with a dedicated DC input port (e.g. Motorola SLR5500); sites needing longer backup times | Mission-critical infrastructure; telecoms-grade resilience; large or multi-site deployments |
Key limitation | Switchover is near-instant but not zero; internal batteries may offer limited runtime without upgrade; not all UPS units handle inductive or switch-mode loads well | Requires compatible repeater hardware; battery must be correctly sized; improper installation can damage the repeater or battery | Higher upfront cost and complexity; typically requires specialist installer and ongoing maintenance contract |
Professional installation recommended? | Not always — straightforward installations can be self-managed | Yes — correct fusing, cable sizing and DC polarity are critical | Yes — always |
Should You Program a Backup Radio Channel?
A simple but effective resilience strategy is to programme a direct (simplex) talkaround channel into every radio.
If the repeater becomes unavailable, users can manually switch to this channel and continue communicating directly between radios.
Advantages
- No additional infrastructure required.
- Provides resilience if the repeater develops a fault.
- Useful during planned maintenance.
- Can prove invaluable during emergency situations.
Limitations
- Coverage is significantly reduced.
- Users must remember to change channel.
- Communication is limited by the distance between individual radios.
- It is generally unsuitable as a replacement for repeater coverage across large buildings or campuses.
For many organisations, a backup simplex channel is an excellent addition to a battery backup solution rather than a replacement for it.
Why Quality Batteries Matter
Not all batteries are designed for long-term standby operation.
Professional installations typically use industrial VRLA (Valve Regulated Lead Acid) batteries from recognised manufacturers such as Yuasa.
These batteries provide:
- Maintenance-free operation.
- Excellent standby performance.
- High reliability.
- Published performance characteristics.
- Long design lives of up to 10–12 years under normal float charging conditions.
While premium batteries may represent a higher initial investment, they generally provide lower lifetime ownership costs through improved reliability, longer replacement intervals and greater confidence that they will perform when required.
Don't Forget Ongoing Maintenance
Installing a backup battery is only part of the solution.
Like any standby power system, batteries naturally deteriorate over time, even when rarely used. Without regular inspection and testing, a battery may appear healthy but fail to provide its expected runtime when needed.
A planned maintenance programme should include:
- Visual inspection of batteries, terminals and cabling.
- Verification of charger operation.
- Measurement of battery float voltage.
- Functional mains failure testing.
- Periodic battery capacity testing where appropriate.
- Replacement of batteries in accordance with the manufacturer's recommendations or when testing indicates declining performance.
Routine maintenance provides confidence that the backup system will perform as expected during an actual mains power failure.
The Benefits of Installing Backup Power
Adding backup power to a repeater provides significant operational benefits:
- Continued communications during mains power failures.
- Improved resilience for security and facilities teams.
- Better support for emergency response procedures.
- Reduced operational disruption.
- Improved business continuity.
- Greater confidence in critical communications infrastructure.
- Increased protection for staff and site operations.
Most importantly, it ensures that the radio system remains available when it is most likely to be needed.
Frequently Asked Questions
Not quite. Most standard UPS units — the kind used for computers and servers — will work, but there are a few things to check before buying.
First, confirm the UPS output is a pure sine wave rather than a simulated sine wave (also called modified or stepped sine wave). Some repeater power supplies, particularly switch-mode types, can behave unpredictably on simulated sine wave outputs.
Second, check the VA and watt ratings against your repeater's actual power consumption. A repeater drawing 100–150 W at transmit needs a UPS rated well above that figure to avoid overload.
Third, consider runtime. Many entry-level UPS units carry relatively small internal batteries and may only provide 15–30 minutes of backup at moderate loads. If your requirement is several hours, look for a UPS with an external battery expansion port, or move to a dedicated DC battery solution.
If you are unsure which UPS is appropriate for your specific repeater model, we are happy to advise — no obligation.
It depends on three things: the capacity of the battery (measured in ampere-hours, Ah), the average current draw of the repeater, and the type of battery chemistry used.
As a rough guide, a 100 Ah AGM battery powering a repeater with an average current draw of around 3 A (a mix of standby and active transmit) would give approximately 16–20 hours of usable backup, accounting for a 50% depth of discharge recommended for AGM batteries to preserve battery life.
A lithium (LiFePO4) battery of the same capacity can typically be discharged to 80% of its capacity, extending that figure to 26–30 hours, though at a higher upfront cost.
These are approximate figures. The actual duration will vary based on your specific repeater model, transmit duty cycle, and the load of any ancillary equipment (controllers, duplexers, power supplies) on the same circuit.
In most configurations, handheld and mobile radios will lose coverage across the wide area or multi-floor coverage the repeater was providing. Users in close proximity to one another may still be able to communicate directly (using simplex or talkaround mode) at short range, but the extended coverage the repeater provides will be lost.
For organisations that rely on their radio system for security, emergency response or site-wide coordination, the loss of a repeater during a power outage can have serious operational consequences. This is the core reason backup power should be considered as part of any professional repeater installation.
Yes. The SLR5500 includes a dedicated DC input that accepts 11.0–14.4 VDC (nominal 13.8 V). This allows a standby battery to be connected directly to the unit, either via a compatible DC power supply with battery management or by a direct battery connection using the correct cable and fusing.
Under normal operation the repeater runs from the mains-powered DC supply, which simultaneously maintains the battery at float charge. When mains power is lost, the repeater continues to operate from the battery without interruption or switchover delay.
The SLR5500 can also be operated with no AC connection at all, making it suitable for fully DC-powered or off-grid installations.
There is no universal legal requirement in the UK mandating backup power for commercial radio repeater installations. However, several considerations may make it effectively necessary depending on your organisation:
- If two-way radios form part of your documented emergency response, fire evacuation or lone worker procedures, your insurers or a regulatory body (such as the Health and Safety Executive) may expect communications systems to remain operational during an emergency — which could include a mains power failure.
- Building regulations for certain occupancies (healthcare, high-rise residential, large public venues) may impose specific requirements for emergency communication systems.
- Organisations that have committed to specific service level agreements or business continuity plans may have contractual obligations that require communications resilience.
If you are unsure whether your installation has specific compliance obligations, we recommend consulting your facilities manager, health and safety advisor or a qualified radio system engineer. We can also provide guidance based on your specific use case.
This varies by battery chemistry and how the system is maintained, but as a general guide:
- Sealed lead-acid (AGM/VRLA): 3–5 years under normal float charge conditions. Heat, deep discharge cycles and poor maintenance shorten this significantly.
- Lithium (LiFePO4): 8–15 years, or 2,000–5,000 charge cycles depending on the specific cell specification.
Battery health should be tested under load periodically — at least annually for mission-critical installations — rather than relying solely on voltage readings, which can be misleading on aging batteries. A battery that reads at nominal voltage may fail quickly under the current demand of a transmitting repeater.
For a standard AC UPS connected to a repeater, a competent in-house person with basic electrical awareness can typically manage the installation safely, provided they follow the UPS and repeater manufacturers' guidance.
For a dedicated DC battery backup — particularly where cabling, fusing and charge management need to be designed — we strongly recommend involving a qualified radio engineer or electrical professional. The consequences of incorrect DC wiring (reversed polarity, underrated fusing, inadequate cable sizing) can include repeater damage, battery failure or a fire risk.
For fully DC-powered infrastructure, professional design and installation is always required. This type of system draws on telecommunications engineering disciplines and should not be attempted without appropriate expertise.
If you would like to discuss your specific installation, our team can advise on the right approach.
We Can Help
Every site is different, and there is no one-size-fits-all solution. The ideal backup power system depends on your operational requirements, the criticality of your communications, the expected duration of power outages, your existing infrastructure and your available budget.
Whether you require a simple UPS to ride through short interruptions, a dedicated battery-backed repeater, or a fully redundant DC power system for mission-critical communications, we can design, supply and install a solution tailored to your organisation.
A backup power solution should not be viewed as a one-off installation, but as part of the ongoing lifecycle management of your communications infrastructure. Correct specification, quality components and regular maintenance all contribute to ensuring your radio system performs reliably when it is needed most.
If you would like to discuss your existing radio system, assess your resilience to power outages, or obtain a no-obligation quotation for a backup power solution, please contact our team on 03300 88 17 80 or complete the short form below.
We'll be happy to recommend the most appropriate solution for your operational requirements.