Converting a Floor Scrubber to Lithium: Retrofit Kits, BMS, Chargers, Ballast and Cost Math

Key takeaways

• A safe conversion is a system change: LiFePO4 pack with BMS, matched charger, controller settings and ballast, not just a battery swap.
• Lithium packs are often 150 to 200 lb lighter than the lead-acid set, which can hurt traction and ramp performance unless ballast is added.
• On a single-shift machine the 8-year cost is often close to break-even; multi-shift use and opportunity charging are where lithium clearly pays.
• Confirm the kit is approved for your machine model and ask how it affects the machine warranty before buying.

Converting a floor scrubber to lithium means replacing the lead-acid set with a lithium iron phosphate (LiFePO4) pack that has a built-in battery management system (BMS), switching to a charger with a matching lithium profile, updating the machine's battery type or low voltage settings, and adding ballast if the lighter pack affects traction. Done as a complete kit, it works well. Done as a battery swap alone, it causes faults, false battery gauges and chargers that never finish.

Lithium makes the most sense for machines that run multiple shifts, need opportunity charging, operate where watering is unreliable, or sit in spaces where hydrogen gassing and acid are a problem, such as healthcare and food areas. For a single-shift machine with a well-maintained flooded set, the economics are closer than sales material suggests. The cost model below shows why.

What a retrofit kit should include

A proper conversion kit for a scrubber is model-specific. Look for:

• LiFePO4 pack sized to the battery tray, at the correct nominal system voltage (24 V or 36 V class).
• Integrated BMS with cell balancing, over- and under-voltage protection, over-current protection, and temperature monitoring.
• Matched charger with a lithium profile approved by the battery maker, ideally communicating with the BMS (often over CAN bus) so the BMS controls charging.
• Wiring and connectors compatible with the machine's main battery connector and charger interlock.
• State of charge display or gauge integration, since lead-acid voltage-based gauges read lithium incorrectly.
• Ballast plates or a ballast recommendation, where the weight change matters.
• Installation instructions including any machine controller parameter changes.
• Safety certification for the pack from a recognized test standard for motive batteries (UL 2271 is a common one for this class of battery). Ask for the certificate, not just a logo.

Whole kits from the machine's own manufacturer or an authorized dealer are the lowest-risk path. Third-party kits can be good, but ask for references on your exact model.

The BMS: what it does and why it matters

A battery management system is the electronics inside a lithium pack that monitors every cell and can disconnect the pack to protect it. It is what makes lithium safe in a scrubber, and it is also the source of most conversion surprises.

The BMS will typically disconnect or limit the pack when:

• Any cell voltage goes too low (deep discharge protection)
• Any cell voltage goes too high (overcharge protection)
• Current exceeds its limit (for example a jammed brush motor or a short)
• Temperature is too high, or too low for charging. Many LiFePO4 packs will not accept charge below about 32°F (0°C) unless they have internal heaters.

When the BMS trips, the machine simply goes dead or the charger refuses to start. This is covered in battery not charging. The important point for a conversion: the BMS current limit must exceed the machine's peak draw, including brush motor startup and drive motor current on a ramp. An undersized BMS gives nuisance shutdowns under heavy down pressure.

Charger compatibility

Lithium needs a constant current, constant voltage profile that stops at the battery maker's voltage, with no float, no gassing stage and no equalize. Lead-acid chargers do not do this. Your options:

Lithium charges fast, but only as fast as the charger allows. A 20 A onboard charger on a 150 Ah lithium pack still takes around 7 hours from empty. If faster turnaround is part of the business case, size the charger for it. See battery chargers.

Machine controller and gauge settings

Many modern scrubbers have a battery type parameter in the controller that changes the low voltage cutout and the battery discharge indicator (BDI). Lithium voltage stays nearly flat across most of its discharge and then drops sharply, so a lead-acid gauge shows "full" for hours and then "empty" suddenly, and a lead-acid cutout may stop the machine too early or too late.

Before the conversion:

1. Ask the dealer whether the controller has a lithium or "custom" battery setting and who can change it.
2. Confirm the low voltage cutout is either set for lithium or that the BMS handles cutoff cleanly.
3. Confirm the charger interlock (the circuit that prevents driving while plugged in) still works with the new charger.

If the machine has no lithium setting and the kit maker has no answer for the gauge, expect operators to be confused by the battery indicator.

Weight, ballast and traction

This is the most overlooked part of a lithium conversion. A lead-acid set is heavy by design, and machine makers account for that weight in traction, stability and how the scrub deck and squeegee load the floor.

Approximate example for a 24 V walk-behind:

Effects of losing that weight:

• Traction on wet floors. Drive wheels have less normal force, so wheel slip on wet, smooth floors increases, especially on traction-drive machines. See traction drive vs brush assist.
• Ramps. Climbing or descending a wet ramp with less weight on the drive wheels raises the risk of slipping. Check ramps and gradeability.
• Down pressure. On some machines, high down pressure settings push against the machine's own weight. A lighter chassis can lift slightly, reducing traction or effective scrub pressure.
• Balance. On walk-behinds, moving weight changes how the handle feels and how easily the deck lifts on turns.

The fix is ballast: steel or cast plates bolted securely into the battery tray, to the weight and position the kit maker or machine maker specifies. Never use loose bricks, sandbags or unsecured weights. Some conversions deliberately skip ballast on light-duty micro scrubbers where the weight change is small; on a mid or large walk-behind or a rider, ask for the ballast specification in writing.

Cost math: an 8-year Scrubber Guide model

Assumptions (approximate, adjust to your quotes): 24 V walk-behind, 260 operating days a year, $22 per hour loaded labor, electricity $0.15 per kWh.

On one shift, the two are close to even. Change one assumption:

• Two shifts a day: lead-acid cycle count doubles and sets are replaced roughly every 1.5 to 2 years, so 4 to 5 sets over 8 years ($4,000 to $5,000) plus more watering, while lithium remains near one pack if its cycle rating covers it. Lithium wins clearly, often by $1,500 to $3,000 per machine, before counting labor saved by not swapping batteries or idling the machine.
• Poor watering discipline: if lead-acid sets actually die in 18 to 24 months, as is common in fleets that skip watering, lithium wins even on one shift.
• Light use (a few hours a week): lead-acid lasts longer by calendar, and the lithium premium may never pay back.

For the broader comparison, see lithium vs lead-acid and total cost of ownership.

Conversion checklist

• Kit approved for the exact machine model and system voltage
• Pack fits tray with hold-downs; no loose movement
• BMS continuous and peak current ratings exceed machine draw
• Matched or approved lithium charger; lead-acid charger retired or reprogrammed
• Controller battery type and low voltage cutout updated
• Battery gauge reads correctly after one full cycle
• Ballast installed per specification
• Ramp and wet-floor traction test before return to service
• Warranty impact confirmed in writing with the dealer
• Pack certification documents on file; lead-acid set recycled

Frequently asked questions