Most sump pump failures happen at the worst possible moment: during heavy rain, which is also when storms take the power out. A primary pump in perfect condition does nothing without electricity. That gap is what a backup is for.

Upstate homeowners saw this clearly after Hurricane Helene in September 2024, when widespread outages lasted for days while the ground was already saturated.

How a battery backup works

A second pump	Sits in the same pit, usually slightly higher than the main pump, with its own float and its own check valve.
A battery	A deep-cycle battery, commonly AGM or flooded lead-acid, kept charged by a controller.
A charger and controller	Keeps the battery topped up and monitors the system.
An alarm	Sounds when the backup is running, when the battery is low, or when water rises above normal. Some units send phone alerts.

The important thing to understand is that a backup protects against two failures, not one. It takes over during a power cut — and it takes over when the main pump fails for any other reason, such as a stuck float or a burnt motor.

Is it worth it for your home?

Usually yes, if

• The basement is finished, or stores anything you would not want wet.
• The pit has ever come close to overflowing during a storm.
• The crawlspace holds ductwork, the water heater or well equipment like the pressure tank.
• Your area loses power in storms, which covers much of the rural Upstate.
• You are away from home for days at a time.

Probably less necessary if

• The sump pump rarely runs, even in heavy rain.
• You already have a standby generator that powers the sump circuit automatically.
• The space it protects holds nothing that water would damage.

Why water-powered backups do not suit well homes

Water-powered backup sump pumps are often recommended online because they need no battery and run indefinitely. They work by using the pressure of the municipal water supply to create suction in the pit.

It is one of the most common pieces of advice that simply does not transfer from city homes to well homes.

How long will a battery backup run?

It depends on three things: the battery’s capacity, the pump’s power draw, and how often the pit fills. A pump that runs once an hour will last far longer than one that runs every few minutes in a downpour.

Manufacturers publish run-time estimates based on a set number of cycles per hour. Treat them as a best case. For long outages, a larger battery, a second battery, or a generator connection extends the protection. If you already have a generator for the well pump, see generator sizing for a well pump — the sump pump can often share it.

Combination and alternative options

• Combination units pair a primary and a battery backup pump in a single pre-assembled system with shared piping.
• A standby generator with an automatic transfer switch powers the primary pump directly, along with the well pump and the rest of the house.
• A portable generator works if someone is home to start it and connect it safely.
• A high-water alarm on its own costs very little and at least tells you the pit is rising.

Keeping a backup ready

A backup that has not been tested is not really a backup.

• Test it every few months. Unplug the primary pump and pour water into the pit until the backup starts.
• Check the battery. Most controllers show its status. Flooded batteries need their water level checked.
• Replace the battery on schedule. Deep-cycle batteries typically last a few years, often around three to five, and lose capacity long before they fail outright.
• Keep the pit clean. Both pumps share it, and clay and debris affect both. See sump pump not working for the routine.

What to remember

1	It covers two failures. Power cuts and a failed main pump.
2	No water-powered backups on a well. They need city pressure you will not have.
3	Run time is a best case. Heavy rain drains the battery faster.
4	Test it every few months. Unplug the main pump and pour in water.
5	Replace the battery on schedule. They fade quietly before they fail.

Frequently asked questions

Is a battery backup sump pump worth it?

For finished basements, crawlspaces that have taken on water before, or homes that lose power in storms, usually yes. It protects against both power cuts and failure of the main pump.

How long will a battery backup sump pump run?

It depends on the battery’s capacity, the pump’s draw and how often the pit fills. Manufacturer figures assume a set number of cycles per hour; heavy rain will shorten that. Larger or additional batteries extend it.

Can I use a water-powered backup sump pump on a well?

No. Water-powered backups rely on municipal water pressure. On a well, the well pump stops during a power cut, so there is no sustained pressure to run them.

How often should I replace the backup battery?

Deep-cycle batteries commonly last around three to five years, depending on type and use. Test regularly and replace before capacity has faded too far.

Does a battery backup replace the main sump pump?

No. It is a second pump that takes over when the main pump cannot run. The main pump still does the everyday work.

Can a backup be added to my existing sump pit?

Usually, as long as the pit has room for a second pump and float. Some installations need a larger pit or modified piping.

Is a generator better than a battery backup?

A standby generator with an automatic transfer switch protects the whole house, including the well pump, but it costs considerably more. A battery backup protects only the sump, and also covers a failed main pump.

See our sump pump repair page, and what to check on the well after a power outage.