You need a battery backup if losing your sump pump would flood a room you care about. The main pump stops in a power outage or a pump failure, and a backup takes over. Zoeller recommends one where power outages are likely or a basement is finished. Pump makers also advise a high-water alarm.
What does a battery backup do?
A battery backup is a second pump, usually a 12-volt DC pump, that sits in the same pit as your main pump and runs from a battery. Zoeller explains: "A battery backup sump pump provides additional protection against flooding during a power outage. It operates on a charged battery and takes over if the primary pump fails or loses power."
Zoeller's instructions for its DC backup system describe the purpose the same way: "This system is a backup to your primary sump pump. It is designed to protect against flooding during power outages or primary pump failure."
That second phrase is worth noticing. A backup protects against two different problems. One is a power outage. The other is a primary pump that has failed for any reason, such as a stuck float or a burned-out motor. So a backup helps even when the power is on.
Zoeller adds that its backup system "will automatically activate when the primary pump fails or if the water level rises above a certain level during a flood, ensuring continuous operation." It also says to make sure the backup is tested regularly and maintained according to the instructions. A backup that has never been tested is a guess, not a safeguard. The bucket test in our guide on how to maintain and test a sump pump works for the backup too, and Zoeller's DC controller is built to give a fault alarm if something is wrong.
When is a battery backup worth having?
Zoeller's guidance is direct. It says: "We recommend having a backup system if your area is prone to power outages or if your basement is finished or used as a living space."
Other authorities point the same way:
- The CDC's advice for getting a home ready for a flood includes "buy and install sump pumps with back-up power."
- Wayne's manual says "an independent highwater alarm or back up pump should be used when risk of property damage from high water levels exists."
- Liberty Pumps' manual says to "consider the addition of a back-up pump" and an alarm "in applications where loss of pump function could result in property damage." It adds that if an alarm is used, it must be connected to a separate electrical circuit.
Put together, the test is the size of the damage. Ask what happens if the pit overflows: would water reach finished flooring, stored belongings, a water heater, or electrical equipment? If yes, a backup is worth having. If the answer is a wet slab that dries, it is less pressing.
For most Arizona homes the question doesn't come up, because most have no sump pump at all. Our guide on whether an Arizona home needs a sump pump explains when one makes sense. If you have a below-grade room with a pump, the risk from a power failure is the same here as anywhere else. Our guide on how monsoon season affects plumbing covers other storm-season checks worth doing before the rain.
How long does a battery backup run?
It depends on the battery and how much water is coming in, so there is no single answer. Zoeller gives a useful reference for one product. Its DC backup system lists a continuous running time of 5.5 hours with the recommended battery. The instructions recommend "a deep-cycle, 12 volt, 90 amp-hour or larger marine battery," and say a 100-plus amp-hour battery will provide approximately 5.5 hours or more of continuous pumping time in an installation with 8 feet of head pressure. They add: "In most installations, the pump runs intermittently and the battery life is extended accordingly."
So a backup is built to cover an outage of hours, not days. Zoeller's DC backup instructions say a completely drained battery may need up to 24 hours for a full recharge once power returns. If your area can lose power for a long stretch during a storm, ask about a larger battery, a second battery, or a different type of backup. Zoeller also sells a water-driven backup, which runs on city water pressure and no battery. Zoeller's FAQ notes that these pumps typically run during heavy rainfall and that the amount of water they use depends on the pump's efficiency, the size of the pit and how often the pump activates.
What can a battery backup not do?
A backup is not a cure-all. Know its limits.
It needs maintenance. Batteries wear out. Zoeller's instructions say: "It is the owner's responsibility to check the battery and battery connection at least once a month." Zoeller's instructions say its batteries carry a 3 year warranty, and Liberty's manual says it warrants its StormCell batteries for 1 year from the date of purchase. Plan on replacing the battery before it fails.
It does not fix a bad discharge. A backup pump that has to push water through a blocked or leaking discharge line will fail the same way the main pump does. Check the check valve and the discharge line. Our guide on how to maintain and test a sump pump covers those checks.
It does not handle sewage. A sump pump and its backup move clear groundwater. Wayne says plainly, "DO NOT USE SUMP PUMPS TO HANDLE RAW SEWAGE." If you have a bathroom or laundry below the sewer line, the pump you need is a sewage ejector, and it has different backup options. See the difference between a sump pump, an ejector pump and a lift station.
It can be undersized. Wayne's chart lists "excessive inflow or pump not properly sized for application" as a cause of a pump that will not shut off. A backup pump has its own capacity. Zoeller's DC backup lists a performance of 35 GPM at 10 feet at 12.7 volts, and your discharge height and your inflow will change what you actually get.
It should have an alarm. Zoeller's DC controller is described as self-testing: if the pump is unplugged or jammed, a fault alarm sounds, and a missing float switch sets off an alarm too. Any backup you buy should tell you when something is wrong, because a backup nobody checks is not a backup. Wayne and Liberty both advise an independent high-water alarm. If yours is already sounding, see why a sump pump alarm goes off.
### What should you do next?
If you have a sump pump and a room below it that matters, add a backup and an alarm. If you already have one, test it on a schedule and write the date you replaced the battery on the battery itself.
A backup does not replace the main pump. If your main pump won't run, see why a sump pump is not turning on. If it runs nonstop, see why a sump pump runs constantly.
HQ Plumbing and Air can install a battery backup or replace a worn pump. We give free estimates, quote the price up front, and are available 24/7.