Whilst many are embracing the benefits of lithium, there is still an extensive installation base of lead acid batteries in critical networks across Australia. In some cases, replacing these VRLA banks entirely may be impractical due to cost, downtime, or the operational disruption it would cause. For certain telecommunications operators, there is another option: combining lithium-ion technology with existing VRLA systems to achieve extended runtime and improved site resilience.
This approach has already been successfully adopted by a Tier One Australian-based telecom operator as part of their network upgrade program. In this case, Polarium lithium batteries were integrated alongside existing VRLA banks to provide additional backup time for key backhaul systems, even after the VRLA batteries had reached their low voltage disconnect point.
Why Consider a Mixed Battery Chemistry Approach?
For telecommunications operators, upgrading power backup is often a balance between technical benefit, cost, and operational disruption. In many cases, replacing an entire VRLA battery bank with lithium can be expensive and logistically challenging, particularly across a large network of remote or difficult-to-access sites.
Key drivers for considering this approach include:
1. Extended Runtime Without Full Replacement
By adding a Polarium lithium bank alongside the existing VRLA system, operators can gain several additional hours of autonomy without the cost of a full system change-out.
2. Handling Increased Site Load
Network upgrades often add radios, transmission equipment, and auxiliary systems that increase power consumption. Mixed-chemistry systems allow the site to meet new runtime requirements without replacing the VRLA bank prematurely.
3. Cost Efficiency
Leveraging the existing VRLA investment while adding lithium capacity can defer a full battery replacement cycle, maximising return on assets already in the field.
4. Reduced Downtime and Installation Complexity
Integrating a lithium bank can often be done without shutting down the site or reconfiguring rectifier voltage settings. This minimises service interruptions for critical telecom infrastructure.
5. Improved Resilience
The lithium bank can be set to take over once the VRLA bank has reached its low voltage disconnect, ensuring continued operation during prolonged outages. This is particularly valuable for sites in disaster-prone or remote areas.
6. Polarium-Specific Safety Advantage
Unlike many lithium solutions, Polarium’s advanced BMS and integrated CLD allow safe parallel operation with VRLA. This ensures protection against overcharging, thermal runaway, and unsafe current flow between banks.
Why Voltage Compatibility Matters
Polarium’s SLB48 modules can be configured in 13-cell, 14-cell, or 15-cell arrangements depending on the required voltage window. While 14-cell configurations are more common due to their slightly higher capacity, in this application a 13-cell variant was selected to match the existing VRLA bank’s float voltage profile. This ensured that both battery types operated within the same voltage range without the need to adjust the site’s rectifier settings.
When the rectifier system is in normal operation, it maintains both the VRLA and lithium banks at their respective float voltages. The lithium module’s internal Current Limiting Device (CLD™) provides cell-level protection and charge management, while the VRLA bank continues to operate according to its original parameters.
The Role of Blocking Diodes and Low Voltage Disconnects
To prevent the two battery banks from feeding into each other, blocking diodes are installed on each bank. This ensures that each chemistry only discharges into the load, not into the other battery bank.
Optional Battery Low Voltage Disconnects (BLVDs) are used in many systems to protect the batteries from excessive discharge. In this configuration, once the VRLA BLVD activates, the VRLA bank is isolated and the Polarium lithium bank takes over, delivering energy down to a much lower state of charge. When mains power is restored, the VRLA BLVD reconnects, allowing the rectifiers to recharge both banks simultaneously.
Thinking Outside the Box
This solution is not possible under AS 5139-compliant energy storage systems and is intended purely for telecommunications shelters, huts, and other controlled facilities. It is also not achievable with most lithium-based batteries on the market, due to safety and control limitations.
The key enabler in Polarium’s design is the combination of its advanced Battery Management System (BMS) and the integrated CLD, which actively limits charge current to prevent overcharging and over-temperature events. This allows the lithium bank to operate in parallel with VRLA safely and reliably, providing site operators with a powerful new tool for extending runtime without full system replacement.
Talk to the Powerbox team today to see how a mixed-chemistry backup configuration can give your sites the extra runtime they need while making the most of your existing VRLA investment.
