Can I switch my −48 V plant from lead-acid to lithium? The 12-point checklist
It depends on your plant, not on the battery brochure. Twelve items decide it, and two of them — temperature compensation left enabled and controller firmware below the version that unlocks the lithium settings — account for most failed retrofits. This checklist tells you what to read off your equipment; it does not declare any plant compatible.
Before you order: the two that fail most retrofits
Most lithium retrofits on −48 V plants that go wrong do so for one of two reasons: temperature compensation is left enabled, or the controller firmware is below the version that lets you set the charge voltage and current the battery needs. Neither shows up on the day of commissioning if somebody checked first — so check items 3 and 6 before anything is ordered.
The 12-point checklist
Work through it with the module label, a photo of the whole shelf and the datasheet of the battery you were quoted. Every reference value below is the one we publish elsewhere on this site, with its source.
| What to check | Why it matters | Reference value | Read more |
|---|---|---|---|
| 1. Identify the plant Photograph the label on a rectifier module and the whole shelf, including the controller. |
The controller generation decides more about what you may install than the module marking does. | Module part number, e.g. 241115.105 · R48-2900U | How do I identify my 48 V DC plant? → |
| 2. Battery architecture: 15S or 16S Ask the battery supplier for the cell count and the full-charge voltage, in writing. |
A 16S (51.2 V) pack at full charge asks for 57.6 V, above the −57.0 V upper limit of the −48 V service range. A 15S (48 V) pack asks for 54.0 V. | 15S for a telecom retrofit · −40.5 V to −57.0 V (ETSI EN 300 132-2) | Can I put a 51.2 V rack battery in my −48 V plant? → |
| 3. Controller firmware version Read the version in the controller display menu — do not infer it from the model. |
Below the minimum version, the settings a lithium bank needs are simply not available. It is a condition of entry, quoted as an upgrade, not worked around. | Read in the controller menu | Does my controller need a firmware update? → |
| 4. Rectifier output range Confirm the adjustable minimum and maximum of the exact module variant in the shelf. |
The lithium setpoint has to sit inside what the module can actually deliver. | ≈43.5–57.6 V on a Flatpack2 48/2000 HE | What float voltage do I set for lithium on a Flatpack2? → |
| 5. Charge profile Set float and equalize to the same value, taken from the battery datasheet; automatic equalize off. |
Lithium is not equalized. The factory default of many plants (53.5 V) is a lead-acid value. | Typically 52–55 V, from the battery datasheet | Lithium float voltage → |
| 6. Temperature compensation Set the compensation sensor to None in the controller — unplugging the probe is not enough. |
It is one of the two settings that most often makes a lithium retrofit misbehave. | Compensation sensor = None | How do I disable temperature compensation? → |
| 7. Plant thermal runaway management Turn the plant's battery thermal runaway function off. |
Thermal protection belongs to the BMS, which measures the cells directly. | BTRM off | Compatibility check → |
| 8. Charge current limit and string capacity Enter the string capacity (module Ah × number of modules) and enable a charge current limit. |
A plant sized for VRLA will otherwise push more current than the pack wants. | 0.1C–0.5C depending on the battery · 4 × 100 Ah → 400 | How do I size a lithium bank to replace my VRLA string? → |
| 9. Low-voltage disconnect Set the plant LVD above the battery's own disconnect, and below any generator start threshold. |
The plant should open first; the BMS is cell protection, not your load-shedding mechanism. | ≥ battery LVD + 0.5 V · practical floor ≈38 V | Where do I set the low-voltage disconnect? → |
| 10. Walk-in and module default voltage Enable soft start and set the module default voltage. |
A plant returning after a long outage should not slam full current into a cold bank. | Walk-in enabled · module default voltage set | Settings gated by firmware → |
| 11. BMS communication and alarms Decide whether you are buying dry-contact alarms or a data link (protocol, cable, BMS version). |
Without a data link the controller shows no state of charge or state of health; protection stays with the BMS either way. | RS485/Modbus · some packs also expose CAN | How does a lithium BMS talk to a DC plant? → |
| 12. Mechanical fit, protection and migration Check rack units, depth, terminals and torque, cable section and breaker; plan how the old string leaves. |
The old breaker was sized for a battery that is leaving the cabinet, and running VRLA and lithium in parallel is a different plan from keeping VRLA as a spare. | Confirmed per site, from the shelf photo | Can I reuse the old breaker? → |
The window everything turns on
Telecom equipment on a −48 V bus is specified to a normal service range of −40.5 V to −57.0 V (ETSI EN 300 132-2). Items 2, 4, 5 and 9 are all ways of keeping a lithium bank, at full charge and at end of discharge, inside that window.
What this checklist does not do
It does not declare your plant compatible, and it does not tell you which firmware version your controller needs: both depend on the exact controller and are read off the equipment, not off a web page. If the twelve answers are filled in and signed for your site, that is the compatibility sheet the audit produces.
Equipment this guide covers
Common questions about this family
Is lithium a drop-in replacement for a VRLA string on a −48 V plant?
No. The bank, the controller settings and often the controller firmware change together. A 15S lithium pack can sit inside the −48 V service range, but only once the charge profile, temperature compensation, current limit and low-voltage disconnect are set for it.
Can I keep the same amp-hours as the old lead-acid string?
Not by copying the nameplate. Size from the site's load in amps and the autonomy you need in hours, using the discharge table of the specific battery at your actual current.
Can you tell me from this page whether my plant is compatible?
No. This page lists what has to be determined. The answer comes from reading your rectifier, controller and firmware version — that is what the compatibility audit documents and signs for your site.
Limitations
General engineering practice on −48 V DC plants. Always confirm values against the datasheets of the specific rectifier module, controller and battery model, and the plant maker's lithium application guidance. The checklist states what has to be determined; it is not a verdict for any site.
Sources
- ETSI EN 300 132-2 — Power supply interface at the input of ICT equipment; Part 2: −48 V DC (normal service range −40.5 V to −57.0 V)
- Datasheet of the specific rectifier module and of the specific battery model quoted (no public URL — cite by title)
- User manual of the installed controller, for the firmware version actually running (no public URL — cite by title)
Editorial and technical methodology →
Other guides
- Is the Emerson R48-2900U the same as the Vertiv R48-2900U?
- Can I mix R4850G2 and R4875G1 modules in the same shelf?
- What float voltage do I set for lithium on a Flatpack2?
- Can I put a 51.2 V rack battery in my −48 V telecom plant?
- How do I disable temperature compensation on a NetSure controller?
- Is the Eltek Flatpack2 discontinued?
- Where do I set the low-voltage disconnect on a lithium retrofit?
- What paperwork does a telecom lithium battery need to ship?
- How do I identify my 48 V DC plant?
- Does my controller need a firmware update before a lithium retrofit?
- How does a lithium BMS talk to a telecom DC plant?
- How do I size a lithium bank to replace my VRLA string?
- Does the grounding scheme change when I retrofit a −48V plant to lithium?
- Can I reuse the old breaker when I swap VRLA for lithium?
- Can a VRLA string and a lithium string run in parallel during a migration?