Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
Summary
A sump pump's battery backup only earns its place during the exact event most likely to defeat the primary pump: a storm that cuts the power. It sits untested for months at a time, because testing it on purpose means creating a small power cut, and most people never do that. This page walks through that test, whether the system is branded Zoeller, Liberty Pumps, or just called a basement watchdog by the people who own it: disconnect the main power, let the battery run the pump alone, and watch it do the job it exists for. It also covers a monthly look at the battery itself, since a corroded terminal or a battery near the end of its life is the most common reason a backup system fails on exactly the night it is needed.
This page does not print a battery group size, a charger output rating, or a maximum pumping height, because those numbers are different for every make of backup system, and the label on your unit or your own installation manual has them. It does not cover installing a new backup system, only testing and checking one that is already in place. Two manufacturer manuals were read for this page, one from Zoeller and one from Liberty Pumps, and on how often to test they disagree; that disagreement is printed here rather than averaged away or quietly picked for you.
Safety
DO NOT TOUCH THE BACKUP PUMP OR THE WATER WHEN THE SYSTEM HAS ELECTRICAL POWER.
Contact with a live part through water can kill you.
KEEP THE BATTERY AWAY FROM A CARBON MONOXIDE DETECTOR.
THE BATTERY CAN RELEASE A GAS THAT CAUSES A FALSE ALARM.
Necessary equipment
| Item | Note |
|---|---|
| Rubber gloves | The gloves protect your skin from battery acid and from pit water. |
| Flashlight | A sump pit is a dark space. |
| Bucket | Use the bucket to carry water to the sump pit. |
| Old towels | The towels keep the water off the floor. |
| Notebook or maintenance record | Record the date of each test. |
| Clean water material | Water from a tap works for this test. |
Prepare the area
Estimated 3 min to 5 min
PUT ON THE GLOVES BEFORE YOU TOUCH THE BATTERY.
Battery acid can burn your skin.
PUT ON THE GLOVES BEFORE YOU TOUCH THE SUMP PIT.
Water in a sump pit can carry bacteria.
- Put on the rubber gloves.<1mReport a problem with step 1, Prepare the area
- Find the backup system next to the sump pit.1mReport a problem with step 2, Prepare the area
- Put the old towels around the sump pit.<1mReport a problem with step 3, Prepare the area
- Remove the cover from the sump pit.<1mReport a problem with step 4, Prepare the area
- A cover keeps debris out of the pit.
- A cover helps to prevent an accident.
Disconnect the electrical power
Estimated 1 min
DO NOT TOUCH A PLUG WITH WET HANDS.
Water on your skin can cause a fatal shock.
- Unplug the primary pump from its outlet.<1mReport a problem with step 1, Disconnect the electrical power
- Unplug the backup charger from its outlet.<1mReport a problem with step 2, Disconnect the electrical power
- The battery must run the backup pump alone during this test.
- Make sure that your hands are dry.<1mReport a problem with step 3, Disconnect the electrical power
- Make sure that the floor near the outlets has no water on it.<1mReport a problem with step 4, Disconnect the electrical power
Examine the battery and the float switch
Estimated 3 min
Source: Model 441 Battery Back-up System, 12 Volt Emergency Sump Pump System, Installation Manual (document 4414000F) · tier 1 · accessed 2026-08-03
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Look at the battery box.<1mReport a problem with step 1, Examine the battery and the float switch
- A shelf or a pad under the box helps to prevent damage.
- A dry location helps to prevent damage from a flood.
KEEP A METAL TOOL AWAY FROM THE BATTERY TERMINALS.
Contact between the two terminals can cause burns and can start a fire.
KEEP SPARKS AWAY FROM THE BATTERY.
KEEP A FLAME AWAY FROM THE BATTERY. THE BATTERY CAN RELEASE A GAS THAT CAN EXPLODE.
- Open the battery box.<1mReport a problem with step 2, Examine the battery and the float switch
- Look at the battery terminals for corrosion.<1mReport a problem with step 3, Examine the battery and the float switch
- Look at the battery cables for damage.<1mReport a problem with step 4, Examine the battery and the float switch
- A cable must have no exposed wire.
- Make sure that the battery is a lead-acid type.<1mReport a problem with step 5, Examine the battery and the float switch
- This charger works with a lead-acid battery only.
- A lithium battery is not correct for this charger.
- Close the battery box.<1mReport a problem with step 6, Examine the battery and the float switch
DO NOT USE A METAL TOOL ON THE FLOAT SWITCH.
THE BATTERY KEEPS THE PUMP CIRCUIT LIVE. THIS IS TRUE EVEN WHEN YOU DISCONNECT THE MAIN SUPPLY. A METAL TOOL CAN CARRY A SHOCK TO YOUR HAND.
- Move the float switch of the backup pump through its full travel with a gloved hand.<1mReport a problem with step 7, Examine the battery and the float switch
- The float must move freely.
- The float must have clearance from the side of the pit.
Do the fill test
Estimated 6 min to 7 min
- Keep your hands away from the sump pit.<1mReport a problem with step 1, Do the fill test
- Pour water slowly into the sump pit.1mReport a problem with step 2, Do the fill test
- Continue to pour water until the float of the backup pump rises.2mReport a problem with step 3, Do the fill test
- Make sure that the backup pump starts.<1mReport a problem with step 4, Do the fill test
- Make sure that the alarm sounds.<1mReport a problem with step 5, Do the fill test
- Make sure that water flows from the discharge pipe outside the building.1mReport a problem with step 6, Do the fill test
- Make sure that the water level decreases.<1mReport a problem with step 7, Do the fill test
- Make sure that the backup pump stops after the float drops.<1mReport a problem with step 8, Do the fill test
- Listen for unusual noise from the backup pump.<1mReport a problem with step 9, Do the fill test
After the test
Estimated 5 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Press the Silence button on the charger or the controller.<1mReport a problem with step 1, After the test
- Your instructions explain the length of the silence.
- Plug the backup charger into its outlet.<1mReport a problem with step 2, After the test
- Plug the primary pump into its outlet.<1mReport a problem with step 3, After the test
- The primary pump and the charger must use separate circuits.
- Make sure that the primary pump starts and lowers the water level.<1mReport a problem with step 4, After the test
- Look at the lights on the charger.<1mReport a problem with step 5, After the test
- The lights show the state of the battery and the power supply.
- Your charger instructions explain each light.
- Install the cover on the sump pit.<1mReport a problem with step 6, After the test
- Remove the gloves. Wash your hands.1mReport a problem with step 7, After the test
- Record the date of the test.<1mReport a problem with step 8, After the test
- Read the test interval from your instructions. Do this test again at that interval.<1mReport a problem with step 9, After the test
Terminology
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
- battery backup
- Also called: backup sump pump, battery backup sump pump, emergency sump pump, sump pump battery, basement watchdog
- float switch
- Also called: float, float ball, tether switch, level switch, bobber
- deep-cycle battery
- Also called: marine battery, backup battery, sump pump battery, sealed battery
- battery charger
- Also called: trickle charger, charging unit, battery maintainer, charger box
- sump pit
- Also called: sump basin, sump hole, sump well, crock, the hole in the basement floor
When to use a professional
Stop if the backup pump does not start during the test. Stop if the alarm does not sound. Stop if the battery does not keep a charge. Speak to a licensed electrician or a pump dealer.
Do not open the pump. Do not open the charger. Do not repair a battery. The pump makers say that a qualified service center must repair the charger or the pump.
A used battery is hazardous waste. Take a used battery to a hazardous waste site or a battery store. Do not put a battery in household trash.
Never work in a wet basement while the system has electrical power. Speak to a licensed electrician about the outlet for the charger. A ground-fault circuit interrupter on that outlet gives more safety. A licensed electrician must change the outlet.
Common questions
How often should I test my sump pump battery backup?
The two manufacturer manuals used for this page do not agree. Zoeller's AquaNot Spin 508 instructions ask for a test at least every three months. Liberty Pumps' Model 441 manual asks for a test every month. This page does not pick one figure over the other or average them. Read your own installation manual for the number that applies to your system, and if you cannot find it, test monthly rather than quarterly.
How do I test a sump pump battery backup?
Disconnect the primary pump and the backup charger, so the battery has to run the pump on its own, the way it would during a power cut. Pour water into the sump pit until the backup pump's float switch rises. The backup pump should start, an alarm should sound, and water should reach the discharge outlet outside the building. Reconnect the charger and the primary pump afterward and confirm the primary pump returns the water to its normal level.
What kind of battery does a sump pump battery backup need?
Both manufacturers call for a 12-volt, deep-cycle, lead-acid battery, in a wet-cell or an AGM design, and both reject a battery built for any other voltage. The exact group size and capacity are different for every system, so read the number from your own installation manual rather than from this page. Neither manufacturer recommends a gel battery, and neither charger is built for a lithium battery.
Can I use my car battery in an emergency?
The manufacturers disagree here too. Zoeller's installation instructions say plainly not to use an automotive battery. Liberty Pumps' manual allows a car battery as a temporary measure once the deep-cycle battery has run down, with the deep-cycle battery put back as soon as possible, and it warns that a car battery has a lower reserve capacity and can fail early under repeated charging. Follow the instructions for your own system rather than this page.
Why does my carbon monoxide detector go off after a power outage?
A lead-acid battery releases gas while it charges, and that gas can set off a carbon monoxide detector even when no carbon monoxide is present. Liberty Pumps recommends at least fifteen feet between a carbon monoxide detector and its own battery charger. Zoeller recommends moving the battery as far from the detector as possible, or venting the battery outside the building. Treat every alarm as real first and follow the detector's own instructions; only suspect the battery once you are sure no carbon monoxide is present.
The alarm on my basement watchdog or battery backup pump keeps going off. What does it mean?
An alarm usually means one of three things: the backup pump has run, the battery charge is low, or the battery has failed. Most systems let you silence the alarm for a set number of hours, but silencing it does not fix the cause. If the alarm returns after every charge cycle, or the battery will not hold a charge, replace the battery. Your own instructions list the exact meaning of each light and each alarm pattern for your system.
Related procedures
- How to clean out a sump pump pit and check the check valve so the pump stops cycling
- How to test a sump pump and its float switch before the wet season
Sources
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
- Tier 1AquaNot 508 Spin, 12 Volt DC Battery Backup Pump, Installation Instructions (form FM3166, P/N 155922-D)
- Tier 1Model 441 Battery Back-up System, 12 Volt Emergency Sump Pump System, Installation Manual (document 4414000F)
Revision history
Current version 1 · updated 2026-08-03 · next review due 2027-08-03
- v1 · 2026-08-03First draft. Built from two manufacturer documents read directly from the publishers' own sites: the Zoeller AquaNot Spin 508 installation instructions (form FM3166, 0822) and the Liberty Pumps Model 441 battery backup installation manual (document 4414000F, 2025). Neither manual had been read for this repository before; they are distinct from the primary-pump manuals already cited by data/procedures/test-a-sump-pump.json. Two genuine manufacturer disagreements are published rather than resolved: the test interval (Zoeller 3 months, Liberty monthly) and whether an automotive battery is acceptable in an emergency (Zoeller refuses it outright, Liberty allows it as a temporary measure). No battery group size, charger output rating, or maximum pumping height publishes as a page-wide number, because each is per-installation; the record routes the reader to their own manual instead of guessing. The one specification marked verified (12-volt battery) is a value both manufacturers state identically and independently. Every step, hazard, and FAQ answer was written from the meaning of the source material in Simplified Technical English or ordinary English, after both documents were read in full and closed; no sentence is a copy or a close paraphrase of either manual's wording. Registering a source and setting a specification's verified flag are both refused to a delegate under config.json -> models.never_delegate_human, so the two new source entries are held in data/sources-additions-test-a-sump-pump-battery-backup.json for merge into data/sources.json rather than written there directly, matching the precedent set by data/procedures/test-a-sump-pump.json's first revision. Until that merge happens, validate.py is expected to report the sources as unresolved (checks 2 and 3) and the conflict_note as under-attributed (check 2), exactly as the sump pump record's own first run did; that gap is the only thing between this record and a pass.
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Comments and corrections
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.