The storm that fills your basement is the same storm that takes out the power. That is not bad luck, it is the whole problem.
A sump pump without a backup is a device that works reliably right up until the moment it is needed.
Do You Need a Battery Backup Sump Pump?
A battery backup sump pump is worth fitting if a flooded basement would cost more than the unit does. Power cuts and rising groundwater arrive together, so the primary pump is offline exactly when the water is coming in fastest.
Key Takeaways
- Storms cause the flooding and the outage at the same time.
- The backup float sits slightly above the primary float.
- Expect 5 to 7 hours of continuous run on a full charge.
- Use a deep cycle battery, never a car starting battery.
- Replace the battery every 3 to 5 years whether or not it has run.
Backup Options Compared
| Type | Runs on | Best for |
|---|---|---|
| Battery backup | Deep cycle battery | Most homes, outages of hours |
| Water powered | Municipal water pressure | City water, long outages |
| Generator | Fuel | Whole house, if already fitted |
| Second pump on the same circuit | Mains | Pump failure only, not outages |
That last row is the mistake worth avoiding. A second pump wired to the same supply protects against a pump failing, which is the less common problem, and does nothing at all about the power going out.
How the Changeover Works
The backup unit sits in the same pit with its own float positioned a little higher than the primary one. In normal operation the primary pump keeps the level below that float and the backup never sees water.
When the primary stops, whether from a power cut or its own failure, the level climbs, the higher float lifts and the backup starts on DC. It is a deliberately simple arrangement, and the mechanics of the primary unit are covered in our guide to how a sump pump works.
Batteries and Maintenance
- Deep cycle marine or AGM, sized by amp hours for runtime.
- Never a car starting battery, which fails under slow steady draw.
- Replace every 3 to 5 years regardless of use.
- Test before storm season by unplugging the primary pump.
- Check the alarm, since a silent failure defeats the point.
Testing is the step that gets skipped. A backup that has sat charged and untouched for four years is not proven to work, and the only way to know is to pull the plug on the primary and watch the water go down.
What a Backup Cannot Fix
A backup buys hours, not immunity. If the discharge line is frozen, blocked or crushed outside the house, both pumps push against the same closed pipe and the basement fills anyway.
The same applies to a pit that fills faster than either pump can clear, which is a sizing problem rather than a power one and is covered in our guide to reading a pump curve. General flood preparation guidance is published at Ready.gov, and where the water carries waste rather than groundwater, our sewage ejector pump guide covers the right equipment.
Frequently Asked Questions
Are sump pump battery backups worth it?
Sump pump battery backups are worth it if a flooded basement would cost more than the unit does, which covers most finished basements. Storms cause the power cuts and the groundwater at the same time, so the primary pump is offline precisely when it is needed. An unfinished basement with a floor drain is the case for skipping one.
Can you put a battery backup on an existing sump pump?
You can add a battery backup to an existing sump pump, and that is how most are fitted. The backup is a second pump with its own float set slightly higher, dropped into the same pit and tied into the existing discharge. The primary pump stays exactly as it is.
How long will a battery backup last on a sump pump?
A battery backup typically gives around 5 to 7 hours of continuous pumping on a full charge, but real outages last far longer than that because the pump cycles on and off rather than running flat out. Actual runtime depends on how fast the pit refills and the battery’s capacity.
How long will a 100 amp hour battery run a sump pump?
A 100 amp hour battery runs a sump pump for a few hours of actual pumping, though it will cover a much longer outage because the pump only runs intermittently. Work it out from the pump’s current draw and how often the pit fills rather than from the amp hour figure alone.
Will a basement flood if the sump pump fails?
A basement will flood if the sump pump fails and water is still arriving, which is why the failure usually shows up during a storm rather than in dry weather. How fast depends on the water table. A backup pump and a high-water alarm are what turn that failure into an inconvenience.
Backup Systems at Ken’s Distributing
Ken’s Distributing stocks battery backup sump systems, primary sump pumps and check valves alongside the Franklin Electric range and the Monarch water pump range.
Tell us the pit size, the lift to the discharge point and how long outages usually last where you are, and we will size the pump and the battery together rather than selling a kit that runs dry after an hour.