Controller firmware is an entry condition, not a detail

This is the question that decides whether a site is a two-hour job or a project, and it is almost never asked before the battery is ordered.

VOLT48 engineering desk · Published 24 Aug 2026

Key figures at a glance

Parameter	Value	Where it comes from
Charge current limit above 0.25C	Gated by a minimum controller firmware version	Controller firmware condition
Module default voltage and walk-in	Gated by a later version again	Controller firmware condition
Where the version is read	The controller display menu — not inferred from the model	VOLT48 intake
If the plant is below the threshold	Quote the controller upgrade, or decline the site	VOLT48 compatibility audit
Settings that still have to change regardless	Float = equalize · temperature compensation None · BTRM off · LVD ≥ battery LVD + 0.5 V	Plant maker's lithium application guidance

Why firmware gates anything at all

A DC plant controller is not a passive supervisor. It holds the charge profile, the alarm thresholds, the string capacity and the protection logic, and it exposes some of those as adjustable parameters and some as fixed behaviour. Which of them are adjustable is a property of the firmware version, not of the model on the front panel. A lithium retrofit needs several parameters that a lead-acid-era release simply does not expose — so the version is not a compatibility footnote, it is the gate.

The two thresholds you will actually meet

Two come up repeatedly. Setting a charge current limit above 0.25C requires a minimum firmware version on common telecom controllers; below it, the limit you need may not be settable at all. Adjusting the module default voltage and the rectifier walk-in requires a later version again. We deliberately do not publish the specific version strings here — establishing them against your exact controller is what the compatibility audit is for, and a version number copied off a web page into a purchase order is how sites get committed to work that does not fit them.

What an honest quotation does when the plant is below the line

There are exactly two defensible answers, and "we'll try" is not one of them. Either the controller upgrade is quoted as part of the job — with its own cost, its own outage window and its own risk — or the site is declined. What is not defensible is shipping a battery into a plant that cannot be configured for it and discovering that during commissioning, with the site down and the old string already gone.

The settings that change no matter what the version is

Independently of firmware, a lithium retrofit means float and equalize at the same value, automatic equalize disabled, the temperature compensation sensor set to None, battery thermal runaway management off because the BMS owns that, string capacity entered as Ah × number of modules, and the plant low-voltage disconnect at least 0.5 V above the battery's own. The firmware question is about which of these you are allowed to set — not about whether they need setting.

How to check before you commit to anything

Read the controller model and firmware version from its display menu and write both down. Do not infer the version from the model or from the plant's installation date, because controllers get updated in the field and just as often do not. With the version in hand, the answer for your plant is a lookup rather than a discussion — and it is one of the twelve points on the sheet our audit hands over signed.

Equipment this guide covers

Common questions about this family

Can I update the controller firmware myself?

That depends on the platform and on what access the operator has, and it is worth establishing before it becomes urgent. What matters more for planning is that a firmware update is a change to a live plant: it needs a window, a rollback position and someone who has done it before. Treat it as a task with a cost, not as a click.

What if I do not know the firmware version?

Then you do not yet know whether your lithium project is a configuration change or a controller replacement, and those differ by an order of magnitude in cost and risk. It is a one-minute reading at the cabinet display. If nobody can get to the site soon, send us the controller photo and the plant model and we will tell you what still has to be established.