Floor Scrubber Batteries: Chemistry, Runtime and Charging Explained
Floor scrubber batteries explained: flooded, AGM, gel and lithium, voltage and amp-hours, a runtime formula with worked numbers, charging rules and cost per cycle.
Key takeaways
- Most walk-behinds run 24 V packs and many ride-ons run 24 V or 36 V, built from flooded lead-acid, AGM, gel or lithium iron phosphate cells.
- Runtime depends on usable energy divided by motor load, and down pressure is the biggest lever operators control.
- Lead-acid should not be routinely discharged below about 20 percent and should be fully recharged after use, while lithium tolerates partial charging.
- The charger profile must match the battery chemistry, and a mismatch is a leading cause of early battery failure.
- Compare chemistries on cost per cycle and labor, not purchase price alone.
Floor scrubber batteries are deep-cycle packs, usually 24 V on walk-behinds and 24 V or 36 V on ride-ons, built from flooded lead-acid, sealed AGM or gel, or lithium iron phosphate (LiFePO4) cells. They power the brush, vacuum and drive motors. A typical lead-acid walk-behind runs about 2 to 4 hours of wet scrubbing per charge, and lithium packs of similar size run similar or longer and accept quick top-up charges.
Batteries are usually the most expensive wear item on a scrubber and the most common reason a machine "stops cleaning well". This page explains how the chemistries differ, how to estimate runtime from the spec sheet, how charging really works, and how to compare lifetime cost.
Battery chemistries used in scrubbers
| Chemistry | How it works in practice | Maintenance | Typical cycle life (approximate) | Main trade-off |
|---|---|---|---|---|
| Flooded (wet) lead-acid | Liquid electrolyte, vented cells | Water every week or so, equalize periodically, clean terminals | About 500 to 1,500 cycles, high end with excellent care | Lowest purchase cost, highest maintenance, hydrogen venting while charging |
| AGM (absorbed glass mat) | Electrolyte held in glass mat, sealed and valve regulated | No watering | Often toward the lower to middle of the lead-acid range | No watering, but sensitive to overcharge and deep discharge |
| Gel | Electrolyte gelled, sealed | No watering | Similar to or a little above AGM in deep-cycle use | Needs a gel-specific charge profile, slower charging |
| Lithium iron phosphate (LiFePO4) | Sealed pack with battery management system (BMS) | Essentially none at the cell level | About 2,000 to 5,000+ cycles | Higher purchase price, needs matched charger and BMS communication |
Cycle life depends heavily on depth of discharge, temperature and charging habits, so treat these as typical ranges, not guarantees. For the full head-to-head, see lithium vs lead-acid.
Volts, amp-hours and watt-hours
Three numbers on a battery spec matter:
- Voltage (V). The system voltage the machine is designed for. A 24 V pack is often four 6 V batteries or two 12 V batteries in series; 36 V is often six 6 V batteries. You cannot change system voltage without changing the motors and controls.
- Amp-hours (Ah). Capacity. For lead-acid, Ah is quoted at a specific discharge rate, usually the 20-hour rate (C20). A scrubber drains the battery much faster than 20 hours, so the capacity you actually get is lower than the label. This is the Peukert effect. Some suppliers also quote the 5-hour rate (C5), which is closer to scrubber use and is a fairer comparison.
- Watt-hours (Wh). Energy. Volts x amp-hours. This is the number to compare across voltages: a 24 V 240 Ah pack and a 36 V 160 Ah pack both store about 5,760 Wh nominal.
When comparing machines or quotes, ask for the Ah rating and the rate it was measured at. Comparing a C20 lead-acid number with a lithium number (which barely changes with rate) overstates the lead-acid pack.
Where the energy goes
A scrubber has three main electrical loads, plus small ones (pump, controls, lights):
| Load | Typical share of draw | What raises it |
|---|---|---|
| Brush or pad motor(s) | Usually the largest share | More down pressure, rough floor, aggressive pads, worn bearings |
| Vacuum motor | Significant and fairly constant | Running at high vacuum setting, clogged filters (motor works harder in some designs) |
| Drive motor (traction machines) | Smaller on flat floors | Ramps, heavy machine weight, constant stop and go |
| Pump, controls, lights | Small | Rarely a factor |
The brush motor is where operators have the most control. Running the heaviest down pressure setting all shift can cut runtime noticeably compared with the normal setting, which is why many machines offer an eco mode. The down pressure page explains the physics.
Estimating runtime: the Scrubber Guide model
Runtime (hours) = nominal Wh x usable fraction x rate factor / average draw (W)
- Usable fraction: about 0.8 for lead-acid if you stop at roughly 20 percent remaining (going deeper shortens battery life); about 0.9 for lithium, limited by the BMS.
- Rate factor: accounts for capacity lost at high discharge rates. For lead-acid using a C20 rating at scrubber loads, assume roughly 0.75 to 0.85. For lithium, assume about 0.95. If you have a C5 rating, use about 0.95 for lead-acid as well.
- Average draw: the average of all motors over the shift. Typical mid-size walk-behinds draw on the order of 1 to 1.5 kW while scrubbing. Check the manual or ask the dealer for amp draw at your settings.
Worked example
Mid-size walk-behind, 24 V, 240 Ah (C20) flooded lead-acid pack, average draw 1,300 W.
- Nominal energy: 24 x 240 = 5,760 Wh
- Usable: 5,760 x 0.8 = 4,608 Wh
- Rate-adjusted: 4,608 x 0.8 = 3,686 Wh
- Runtime: 3,686 / 1,300 = about 2.8 hours
Same machine with a 24 V, 200 Ah lithium pack:
- Nominal: 24 x 200 = 4,800 Wh
- Usable: 4,800 x 0.9 = 4,320 Wh
- Rate-adjusted: 4,320 x 0.95 = 4,104 Wh
- Runtime: 4,104 / 1,300 = about 3.2 hours, plus the option of a 30 to 60 minute top-up at lunch
The smaller lithium pack runs longer because more of its label capacity is actually usable. Run your own numbers in the battery runtime calculator, and see measured ranges by class in battery runtime data.
Runtime vs work: does it cover the shift?
At 11,400 sq ft/hr practical (a 20 in machine), 2.8 hours covers about 32,000 sq ft. If the nightly route is 40,000 sq ft, the lead-acid machine needs either a bigger pack, a mid-shift swap, or a lighter pressure setting. The lithium option with a 45 minute lunch charge could cover it. That is the real question for a buyer: not "how many hours" but "does it finish the route".
Charging: the rules that decide battery life
Lead-acid (flooded, AGM, gel)
- Charge after every use that takes more than a small fraction of capacity. Leaving lead-acid partly discharged causes sulfation, which permanently reduces capacity.
- Let the charge finish. A full lead-acid charge commonly takes 8 to 12 hours, including the finishing stage. Unplugging early repeatedly leaves the pack chronically undercharged.
- Do not opportunity charge lead-acid routinely. Short top-ups add cycles without completing the finishing stage.
- Water flooded batteries after charging, not before, and only to the level the maker specifies. Use distilled or deionized water. Charging with plates exposed damages them; overfilling before charging causes boil-over.
- Equalize flooded batteries periodically if the charger and maker recommend it. Never equalize AGM or gel.
- Ventilate. Charging flooded lead-acid releases hydrogen. Charge in a ventilated area away from sparks, as your safety program should specify.
Lithium (LiFePO4)
- Use only the matched charger or a charger that communicates with the pack's BMS.
- Partial charging is fine. Opportunity charging at breaks is one of lithium's main benefits.
- Avoid charging below freezing unless the pack has heating; most BMS units block it.
- Store partly charged if the machine will sit for weeks, following the maker's guidance.
Charger profile mismatch
Flooded, AGM, gel and lithium each need a different charge algorithm. Machines are frequently converted from flooded to AGM (to eliminate watering) without changing the charger profile. The result is chronic overcharging or undercharging and a pack that fails in a fraction of its expected life. If you change battery type, change or reprogram the charger at the same time, and label it.
Cost per cycle comparison
Purchase price alone misleads. Divide cost by expected cycles, and add labor.
Scrubber Guide model: cost per cycle = (pack price + install) / expected cycles + maintenance labor per cycle
Illustrative example using variables, because pack prices vary widely by size and supplier:
| Item | Flooded lead-acid | Lithium (LiFePO4) |
|---|---|---|
| Pack price | L | about 2.5 to 3.5 x L (illustrative) |
| Expected cycles | about 1,000 with good care | about 3,000 |
| Pack cost per cycle | L / 1,000 | about 3 x L / 3,000 = L / 1,000 |
| Watering and cleaning labor | About 10 to 15 minutes per week | None at cell level |
| Opportunity charging | No | Yes |
In this illustrative case the pack cost per cycle is roughly equal, and lithium wins on labor and flexibility. If your lead-acid batteries are routinely abused (not watered, not fully charged), real-world life may be far below 1,000 cycles, and lithium wins clearly. If the machine runs only an hour a few days a week, the lead-acid pack may age out from time rather than cycles, and the faster payback of lithium shrinks. Fold this into total cost of ownership.
Signs a battery pack is failing
- Runtime drops noticeably over a few weeks, not gradually over a year.
- Vacuum pickup gets weak late in the shift.
- One flooded cell reads a much lower specific gravity than the rest (hydrometer test).
- Batteries are hot after charging or one battery in the string is visibly swollen.
- The charger reports a fault or fails to finish.
Replace lead-acid batteries as a full set. Mixing a new battery with old ones in a series string pulls the new one down to the condition of the old. Routine checks are listed in battery maintenance.
Frequently asked questions
How long does a floor scrubber battery last per charge?
A lead-acid walk-behind typically runs about 2 to 4 hours of wet scrubbing per charge. Lithium packs of similar size run similar or longer, and they can be topped up during breaks.
How many years do floor scrubber batteries last?
It depends on cycles and care rather than years. Lead-acid packs typically deliver roughly 500 to 1,500 cycles, which is often 2 to 5 years of single-shift use, while lithium iron phosphate packs commonly deliver 2,000 to 5,000 or more cycles.
Can I put lithium batteries in my lead-acid floor scrubber?
Many machines can be converted, but you need a pack designed for the voltage and space, a matched charger, and ideally confirmation from the manufacturer or dealer that the controls and warranty support it. Swapping only the batteries without the charger is a common and costly mistake.
Should I charge my scrubber batteries after every use?
For lead-acid, yes, after any meaningful use, and let the charge complete fully. For lithium, partial and opportunity charging is fine, so charge whenever it is convenient.
Why does my scrubber lose suction near the end of the shift?
As lead-acid batteries discharge, voltage drops and the vacuum motor weakens, which reduces pickup. Consistently weak late-shift pickup usually means the pack is undercharged, aging, or too small for the route.