Floor Scrubber Battery Not Charging: What to Check First

When a floor scrubber battery is not charging, the fault is in one of four places: the power supply, the charger, the connections or the batteries. Check them in that order, because that is the order of cost. A battery set costs far more than a charger, and packs get replaced that were never dead, when the real fault was a tripped outlet, a damaged lead or a corroded terminal.

What is the charger telling you?

The charger’s status lights are the cheapest test you have.

Error codes matter. Chargers separate “battery voltage too low to start”, “battery not connected” and “charge timed out”, and each points somewhere different.

1. The outlet and the charger

Start here because it costs nothing and it is often the answer.

• Is the outlet live? Plug something else into it. Charging areas are often on circuits that get switched off or on GFCI outlets that have tripped.
• Is the charger’s own fuse or breaker intact?
• Is the charging lead damaged? Leads get run over, caught in doors and pulled out by the cable. Check the full length.
• Is the charging connector fully seated? Battery connectors need to be pushed fully home. Half in looks connected and is not.

If the charger shows no sign of life on an outlet you have proven is live, the charger has failed, which is a much smaller bill than a battery set.

2. The connections

This is the check people skip, and it is the one that most often makes a good pack look dead. With the machine off and the key out, look at the battery terminals and cables:

• Corrosion. White or blue-green crust on the terminals acts as an insulator. Enough of it and the charger sees an open circuit.
• Loose terminals. Vibration works them loose over months. A loose terminal has high resistance, gets hot and can melt.
• Damaged or burnt links. The cables between batteries carry the full pack current. If one is damaged, the pack is broken in the middle.
• A blown main fuse. Many packs have an inline fuse near the positive terminal.

Clean corroded terminals, tighten anything loose, and try charging again before you judge the batteries.

Safety before you touch the pack

• A battery pack can deliver hundreds of amps into a short circuit. A tool dropped across two terminals can melt, throw molten metal and cause severe burns.
• Lead-acid batteries give off hydrogen while charging. Hydrogen is explosive. Charge in a ventilated area away from sparks and flames.
• The electrolyte is sulfuric acid, which burns skin and can blind.

OSHA’s rules for forklift battery charging areas, in its powered industrial trucks standard, section (g), are a good model for scrubber charging too: ventilation for the gases, facilities to flush and neutralize spilled electrolyte, fire protection and no ignition sources. Its construction rule on batteries and battery charging requires facilities for quick drenching of the eyes and body within 25 feet of battery handling areas.

• Remove rings, watches and metal bracelets.
• Use insulated tools and wear eye protection.
• Never rest a tool on top of a battery.
• If you are not confident, stop and call a technician.

3. Water level (flooded lead-acid only)

If your batteries have removable caps, low electrolyte stops them charging properly and damages them permanently. The plates must stay covered. Any part of a plate exposed to air is damaged every time you charge.

• Use distilled water only. Minerals in tap water shorten battery life.
• Top up after charging, not before. The electrolyte rises during charging, so a battery filled first can overflow and lose acid.
• Do not overfill. Fill to the level in the manual, not to the brim.
• Never add acid. Only water is lost.

Sealed AGM, gel and lithium batteries have nothing to top up. Do not try to open them.

A hydrometer tells you a lot on flooded batteries: one cell with much lower specific gravity than the others points to a failing battery.

4. The batteries themselves

Only after all of the above. Signs the pack is worn out:

• Run time has been getting shorter for months. That is normal end of life. If a machine that used to run four hours now runs ninety minutes, charging will not fix it.
• The charger finishes in a fraction of the normal time. The pack cannot hold charge.
• One battery reads much lower than the others. In a series pack, one weak battery drags the whole pack down.
• A swollen or distorted case. That battery is finished and is a hazard. Stop charging.
• A rotten-egg smell. The battery is being overcharged or is failing inside. Ventilate and stop charging.

For how long each battery type should last, see how long floor scrubber batteries last.

Replace the whole set, not one battery

If one battery in a series pack has failed, replace the whole set. A pack is only as good as its weakest battery. A new battery next to worn ones is dragged down to their level and ages at their rate, so within months you have the same problem.

The exception is a nearly new pack where one battery failed early for a clear reason, such as a manufacturing fault or physical damage. Then a single matched replacement can work.

Why batteries die early

Well-kept lead-acid scrubber batteries typically last about two to three years at one charge per working day. If yours fail sooner, the cause is usually one of these:

• Partial charging. Plugging in for an hour between shifts without ever finishing a full charge. Battery maker EnerSys warns that frequent partial charging can cut a lead-acid battery’s cycle life by more than half. Lithium batteries handle it; lead-acid batteries do not.
• Leaving the pack flat. A discharged lead-acid battery left sitting sulfates, and sulfation is largely permanent. Charge it the same day.
• Running it until it stops. Deep discharges cut cycle life. Recharge when the battery indicator says so.
• Never checking the water on flooded batteries.
• Charging in a hot room, which speeds up every kind of battery wear.

None of these is a machine fault, and all of them can be fixed with a charging routine. Our floor scrubber maintenance checklist includes one.

Checking order

1. What does the charger show? No lights, never finishing, or finishing at once are three different problems.
2. Is the outlet live and the lead undamaged?
3. Is the charging connector fully seated?
4. Are the terminals clean and tight, and is the main fuse intact?
5. On flooded batteries, are the plates covered?
6. Has run time been falling for months? Then the pack is worn out.

Tools for battery checks

For electrical checks

Klein Tools MM325 digital multimeter

Reads DC voltage, continuity and resistance for battery, cable and motor checks.

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Flooded lead-acid batteries

Battery hydrometer tester, 2 pack

Reads the specific gravity of each cell to find a weak cell. Not for sealed AGM, gel or lithium batteries.

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Related faults

A weak pack often shows up as something else first. The brush motor is usually the biggest load, so it drops out first when voltage sags. If the brush has stopped but everything else works, suspect the batteries. See floor scrubber brush not spinning. If the machine runs but leaves water behind, see floor scrubber not picking up water.

Frequently asked questions

Bottom line: read the charger, then check the outlet, lead, connector, terminals and water level before you blame the batteries. If run time has been falling for months, the pack is worn out, and the fix for the next one is full charges, no partial top-ups on lead-acid, and regular watering.