Why Your SUNMAX Floor Scrubber Battery Dies Early (And How to Fix It)

Section 1: Why Lead-Acid Batteries Fail Early

Lead-acid batteries are reliable, but they are not forgiving. A few common mistakes cause most early failures.

Sulfation

When a lead-acid battery sits discharged — even for a day or two — lead sulfate crystals form on the plates. Over time, those crystals harden and reduce the battery's ability to hold a charge. Sulfation from sitting discharged causes permanent damage that no charger can reverse. This is the single most common cause of early battery death in floor scrubbers.

Undercharging

Pulling the plug before the charge cycle completes leaves the battery partially discharged. Do this repeatedly and the battery never reaches full capacity. It starts every shift already behind.

Low Water Levels

Flooded lead-acid batteries need water to function. The electrolyte solution inside covers the lead plates. If the water drops below the plates, those exposed sections dry out and stop working. You lose capacity permanently. Water should sit at 1/4 inch above the plates, and you should only use distilled water.

Terminal Corrosion

Corrosion on battery terminals increases resistance. More resistance means less power reaching the motor. Your machine runs weaker and the battery works harder than it should.

According to Wisconsin Scrub and Sweep, a well-maintained lead-acid battery lasts 3 to 5 years. Poor maintenance can cut that lifespan by 30 to 50 percent. That means a battery that should last 4 years might fail in under 2.

For more background on this specific issue, SUNMAX has also covered it directly: Why the Batteries of My Floor Scrubber Machine Are Losing Power Quicker Than Before.

Section 2: After-Every-Use Checklist

These three steps take less than five minutes. Do them every single time you finish a shift.

1. Plug In Immediately

Do not leave the machine sitting discharged overnight. Plug it in as soon as you park it. Every hour a depleted battery sits without charging increases sulfation risk. This one habit alone extends battery life more than anything else.

2. Check Water Level After Charging

Always check water levels after a full charge, not before. Charging causes the electrolyte to expand. If you top up before charging, the battery can overflow and spill acid. Check after the charge cycle completes. If the level is low, add distilled water only.

3. Wipe the Terminals

Use a dry cloth to wipe down the battery terminals after each use. Remove any moisture or residue. This takes 30 seconds and prevents the corrosion buildup that quietly kills battery performance over time.

If you operate a SUNMAX walk-behind scrubber, these steps are especially easy to build into your post-shift routine since the battery compartment is accessible without tools.

Section 3: Weekly Maintenance Checklist

Once a week, take 10 minutes to go through these checks.

Inspect the Terminals

Look for white or blue-green buildup around the terminal posts. Light corrosion at this stage is easy to clean. Ignore it and it gets worse fast.

Check Cable Connections

Tug gently on each battery cable. Connections should be tight. A loose cable causes arcing, heat buildup, and inconsistent power delivery. Tighten any loose connections before the next shift.

Inspect the Battery Case

Look at the battery housing. Check for cracks, bulging, or any sign of swelling. Battery swelling is caused by overcharging and means the battery is being damaged internally. A swollen battery needs to be replaced.

Section 4: Monthly Maintenance Checklist

Monthly maintenance goes deeper. Set aside 20 to 30 minutes once a month.

Run a Full Equalization Charge

An equalization charge is a controlled overcharge that helps balance the cells inside the battery. Most quality chargers have an equalization setting. Run it once a month. It breaks down sulfate buildup before it becomes permanent and keeps all cells performing evenly.

Top Up with Distilled Water

Check every cell. Water should sit at 1/4 inch above the plates. Use only distilled water. Tap water contains minerals that contaminate the electrolyte and accelerate plate damage. Never use well water or filtered water from a pitcher — distilled only.

Clean the Terminals with Baking Soda Solution

Mix one tablespoon of baking soda with one cup of water. Apply the solution to the terminals with an old toothbrush. It neutralizes acid corrosion on contact. Rinse with clean water, dry thoroughly, and apply a thin layer of terminal grease or petroleum jelly to slow future corrosion.

Monthly inspection of cables and connections is a standard recommendation from equipment maintenance specialists and keeps small issues from becoming expensive ones.

Section 5: Storage Rules

If your machine sits unused for any stretch of time, storage conditions matter a lot.

Never Store a Discharged Battery

A discharged battery sitting in storage sulfates quickly. Before you park the machine for more than a day, make sure it is fully charged.

Recharge Every 10 Days

Lead-acid batteries self-discharge even when not in use. If the machine sits for more than 10 days, recharge it. Set a calendar reminder if you need to. A battery that drops too low during storage may not recover fully.

Store in a Cool Location

Heat speeds up self-discharge and accelerates plate degradation. Storing the battery in a cool location minimizes self-discharge and extends overall lifespan. Avoid storing near heat sources, in direct sunlight, or in areas that get above 80 degrees Fahrenheit for extended periods.

Section 6: Warning Signs the Battery Is Failing

Sometimes maintenance is not enough. If you see any of these signs, the battery may be at end of life.

• Won't hold a charge past 2 hours of runtime. A healthy battery should power a full shift. If you're recharging mid-shift regularly, capacity has dropped significantly.
• Swollen or bulging case. Physical swelling means internal damage from overcharging or heat. The battery is unsafe and needs replacement.
• Acid smell near the battery compartment. A sulfur or rotten egg smell during or after charging indicates the battery is gassing excessively. This is a sign of a failing or overcharged battery.
• Visible corrosion that returns within days of cleaning. Rapid corrosion buildup suggests the battery is leaking or venting acid. That level of deterioration is not recoverable with cleaning alone.
• Machine runs noticeably weaker than before. If brush pressure feels reduced or the machine slows on inclines it handled fine before, the battery is not delivering full voltage.

If your RT70 is showing these signs and is still within its coverage period, call SUNMAX support directly at 800-788-0856. The team is US-based and can help you diagnose whether the issue is the battery, the charger, or something else.

If you're at the point of replacing the battery and want to eliminate these maintenance requirements entirely, the RT70+ lithium upgrade at $3,499 removes the water-level and equalization requirements that come with flooded lead-acid batteries. Lithium batteries do not sulfate and require significantly less routine maintenance.

FAQs

How often should I add water to my SUNMAX floor scrubber battery?

Check water levels monthly and after every equalization charge. Add distilled water only when levels drop below 1/4 inch above the plates. In heavy daily use, you may need to check more frequently. Never add water before charging — always check after a full charge cycle to avoid overflow.

My RT70 battery is only 8 months old and already losing power. Is it defective?

Not necessarily. Early capacity loss in lead-acid batteries is almost always caused by sulfation from incomplete charging or sitting discharged, low water levels that exposed the plates, or repeated partial charges. Check your charging habits first. If the battery was consistently left discharged overnight or unplugged before the cycle completed, that damage accumulates fast. Contact SUNMAX at 800-788-0856 if you want a technician to help you diagnose it.

Can I use tap water instead of distilled water to top up the battery?

No. Tap water contains minerals and chlorine that contaminate the electrolyte solution inside the battery. Over time, those minerals coat the lead plates and reduce the battery's ability to hold and deliver a charge. Distilled water is inexpensive and available at most grocery stores. It is the only safe option for flooded lead-acid batteries.

Still Running Your Machine Hard Every Day?

If your current battery is past saving and you're ready to replace the machine or upgrade, the RT70 and RT70+ both come with a 2-year warranty and ship from SUNMAX's warehouse in Whittier, CA. US-based technical support and parts are available when you need them.

Call 800-788-0856 to speak with the SUNMAX team directly. They can help you decide whether a battery replacement, a new machine, or a lithium upgrade makes the most sense for your operation.