How Do You Maintain AGM Floor Scrubber Batteries?

AGM and gel floor scrubber batteries never need water, but they still need care. Charge them fully after every session of 30 minutes or more, let every charge finish, keep the charger set to the right battery type, and recharge before the gauge drops below about 20%. Those habits decide whether a sealed pack lasts one year or five.

That's the whole routine, so if your crew already follows it, you can stop here. If your machine's runtime keeps shrinking anyway, the rest of this guide shows you where the usual mistakes hide.

Not sure which battery your scrubber has, or which one you should buy next? The floor scrubber battery comparison covers that. Running flooded batteries instead? Head to the flooded battery maintenance guide.

Why do "maintenance-free" AGM batteries still die early?

Picture your night crew with a sealed walk-behind. The scrubber runs low halfway through the lobby, so someone plugs it in for 15 minutes during the break, unplugs it and finishes the job. It works, so it quietly becomes the routine.

A year later, the machine that used to run for two hours quits after thirty minutes. That exact story shows up on r/Custodians, where one crew cut its runtime to about 30 minutes with mid-shift top-ups, then got well over two hours a year later from a new set just by letting every charge finish.

"Maintenance-free" only means you never add water. Charging is still maintenance, and AGM is less forgiving about it than most crews expect. Tennant rates standard AGM batteries at about 400 charge cycles, roughly a year of expected lifespan, while crews who charge carefully report sets lasting three years or longer. The battery is the same in both cases, and the habits are what change.

How should you charge AGM floor scrubber batteries?

Fully, once per work session, and without interrupting the charging cycle. Three rules cover almost every situation you'll run into.

Charge after every session of 30 minutes or more

Trojan's AGM battery maintenance guide says your batteries should be fully charged after each use, and it defines a use as 30 minutes or more of runtime. So if you scrub the break room for five minutes, you don't need to plug in, but if you scrub for an hour, you plug in as soon as you're done.

Let every charge finish, and skip short top-ups

This is where advice online contradicts itself. Some sources tell you to charge after every shift, some tell you to ration charges, and some tell you to wait until the battery is empty. The real answer comes down to how AGM handles a charge that never finishes.

Trojan explains that some traditional AGM batteries must be fully recharged after each cycle, because running them at a partial state of charge causes sulfation and corrosion that shorten battery life. EnerSys puts a number on it: an AGM battery rated for 700 cycles may drop to 300 if it keeps getting plugged in for short charges. EnerSys sells TPPL batteries, which are built for top-ups, so read that figure as a vendor comparison, although it matches what crews report.

That means a lunch-break top-up costs you twice, because it spends a cycle and it leaves your battery partly charged.

Recharge before the gauge drops below 20%

Trojan recommends never letting an AGM battery discharge more than 80%, a limit known as depth of discharge. On your gauge, that means you plug in while about a fifth of the charge is still left. You may still hear that a battery should run flat before charging, but that advice belongs to old nickel batteries, and Trojan is clear that lead-acid batteries have no memory effect and should not be fully discharged first.

Many scrubbers raise the deck or cut the vacuum at a low-battery cutoff, and you should treat that cutoff as a floor rather than a target. Onboard gauges are approximate too, so when your first warning light comes on, finish the pass and head to the charger.

Is your charger set for AGM or gel?

Check it today, because many smart chargers have separate modes for flooded batteries (often labeled STD), AGM and gel. A practitioner on r/Custodians explains that an AGM battery will technically charge on any of those modes, but the wrong mode won't charge it correctly and wears the cells out early. This bites hardest after a battery swap, when your new AGM set goes into a machine whose charger is still set for flooded or gel.

Gel needs its own setting for a reason: Trojan's battery user's guide recommends a gentler charging current for gel (10 to 13% of rated capacity) than for AGM (20%). The same sources add three more charger rules:

• Never equalize AGM or gel. Trojan warns that equalizing sealed deep-cycle batteries causes permanent damage.
• Use temperature compensation if your charger offers it. Trojan says it should always be used with AGM batteries.
• Never charge a frozen battery, and avoid charging when the battery is above 122°F.

Charging problems also come from chargers that fail in ways that look exactly like dead batteries. A tech in that same Clarke thread describes a charger whose cooling fan died, so it overheated, shut off, cooled down and restarted over and over, never finishing a charge. Before you buy a new set, make sure your charger actually completes its cycle and shows no fault lights.

Why does real AGM battery lifespan range from 1 to 5 years?

Because your batteries spend cycles per charge, not per year. Here is the math on Tennant's 400-cycle rating and on Trojan's claim that its advanced AES AGM line lasts up to 3 times as many cycles as standard AGM:

These are cycle-count estimates rather than guarantees, and they assume every charge finishes. Two more factors push your set toward one end of the range or the other:

• Heat. Trojan notes that batteries working above 80°F deliver more than their rated capacity, but their life is reduced, so a hot battery room quietly ages your set.
• The wrong battery. Batteries Plus warns that a general-purpose AGM battery in a scrubber loses its runtime within a few dozen uses and can overheat and swell. Only deep cycle batteries belong in your tray, so car and marine batteries are out too.

What maintenance checks do sealed batteries still need?

A few minutes of maintenance a month keeps your set healthy:

• Clean, dry tops and terminals. Trojan says to keep terminals clean and dry to avoid corrosion, and recommends cleaning with 1 cup of baking soda per gallon of water, followed by a rinse and a dry cloth.
• Tight terminals at the right torque. Over-tightening can break a terminal, and a loose one can overheat.
• No fluid on top of the battery. Trojan says fluid there may mean your battery is being overcharged, which points you back to the charger.
• Ventilation while charging. Sealed batteries gas far less than flooded ones, but Trojan still says to charge only in well-ventilated areas.

How do you store AGM batteries when the scrubber sits?

Charge your set fully before storage, and keep it somewhere cool and dry. Sealed batteries hold their charge well while parked, and Discover rates its AGM batteries at less than 3% self-discharge per month, compared with up to 15% for flooded. Holding a charge well still isn't holding it forever, so follow Trojan's storage routine:

1. Check the voltage every 2 to 3 months, or every 1 to 2 months if your storage area runs above 90°F.
2. Give the set a boost charge at 75% state of charge or lower, which is about 12.54 volts on a 12-volt battery at rest.
3. Recharge fully before your machine goes back to work.

Cold matters as well. Trojan notes that at 0°F a battery delivers only half its capacity, so a scrubber stored in an unheated building will feel weak until it warms up.

How do you know it's time to replace AGM batteries?

When your runtime stays short even after full, uninterrupted charges on a charger you've confirmed works. Check the charger and cables first, since they cost far less than a new set.

When it really is the batteries, replace the whole set. Trojan explains that in a mixed set, the older batteries need more charge than the new ones, so your new batteries get overcharged while the old ones stay undercharged. One team on r/Custodians writes the install date on every battery, which ends the guessing about how old your set really is.

When is AGM the wrong battery for your crew?

AGM works best when your machine runs one session a day and sits overnight to charge. If your crew genuinely needs mid-shift top-ups, or you run the scrubber across two or three shifts, you'll be fighting AGM's rules every day.

In that case, a chemistry built for top-ups, like TPPL or lithium, fits your schedule better, and the floor scrubber battery comparison shows you how they stack up.

If you're choosing a machine and aren't sure which battery suits your routine, call us at (855) 601-5678 with your square footage, floor type and how often you clean, and we'll suggest a setup. Your order is also covered by our 30-day return policy, and you can browse the full range of floor scrubbers anytime.

FAQ

Can I leave AGM batteries on the charger?

Overnight after a shift, yes, since that's how the charge gets to finish. For long idle stretches, Trojan's guide advises against keeping sealed batteries that cycle often on continuous float charging, so unplug once the charge completes and follow the storage routine above.

Can I swap gel batteries for AGM?

Usually, if the size, voltage and terminals match your machine. The key step is switching your charger to AGM mode, because leaving it on the gel setting won't charge the new batteries correctly.

Can a dead AGM battery be brought back?

Rarely. Don't try to equalize it, since Trojan warns that equalizing damages sealed batteries permanently. If your set won't hold a charge after full charges on a charger you've confirmed works, it's time for a new set, and the floor scrubber troubleshooting guide covers other runtime problems.

Written by Rod Michelini, founder of OneUp Cleaning. We sell AGM, gel, TPPL and lithium machines, so we have no reason to favor one chemistry here. Battery figures come from the manufacturers' own documentation, checked in September 2026.