Sump Pump Backup: Battery vs Generator

Who needs a sump pump backup

You need one if your basement has flooded before, if you have finished space or a furnace down there, or if your area loses power during the same storms that fill the pit. The primary pump usually fails at the worst time: heavy rain, power out, pump running nonstop. A backup covers both failures, the dead pump and the dead grid.

The three options compared

Battery backup sump pumps

A battery backup is a second, smaller pump that sits in the pit next to the main one, on its own float, wired to a controller and a battery. Basement Watchdog's systems start the backup pump automatically for a power outage, a failed main pump, a stuck float, or water coming in faster than the main pump can handle. The controller watches the pump, power and battery around the clock and sounds an alarm when something needs attention.

How long the battery lasts. This is the number everyone asks for, and it depends on how often the pump runs. Angi puts typical backups at 6 to 24 hours, and says a fully charged battery gives about five to seven hours of continuous pumping, or one to three days when the pump cycles on and off. Basement Watchdog rates its systems at 40 to 80 hours, but at a 10% duty cycle, so in a downpour you'll see far less.

Which battery. Basement Watchdog says maintenance-free batteries can be used on its current backup systems, and that standby batteries outlast automotive or deep-cycle batteries in this job. Wet-cell batteries need water added every 4 to 6 months, and lithium-ion isn't supported. Angi prices a standard battery at $100 to $200 with a 3 to 5 year life, and suggests planning on replacement roughly every five years. Write the install date on the battery with a marker. You'll be glad you did.

Capacity. Angi splits systems into low-capacity units up to 1,000 gallons per hour at $200 to $400, and high-capacity units up to 2,200 gallons per hour at $400 and up. If your main pump runs constantly in storms, buy the bigger one.

Combination systems put a primary pump and a battery backup pump on one discharge assembly, sold as one kit. They're a clean option when you're replacing a tired primary pump anyway.

Water-powered backups

These use household water pressure to pull water out of the pit through an ejector. No batteries, few moving parts, and Angi says they can last 10 years or about 20 with upkeep.

The limits are real. They need steady pressure around 40 to 60 psi and run only on municipal water. They use about two gallons of city water for every gallon they remove, which shows up on the water bill. On a well, the well pump stops when the power does, so a water-powered backup does nothing in an outage. Ask your local plumbing inspector whether the supply connection needs a backflow preventer.

Running the sump pump on a generator

A generator keeps the main pump running at full speed for as long as you have fuel. Champion lists a 1/2 HP sump pump at 800 to 1,050 running watts and 1,300 to 2,150 starting watts, so even a small portable can run it.

The weak spot: a portable won't start itself. If the power goes out in the middle of the night, or while you're at work, the basement floods anyway. That's why a generator is best as a partner to a battery backup, not a replacement. The battery covers the first hours, and the generator takes over once you're home and it's running. Wire the sump circuit into an interlock kit or transfer switch setup, or plug the pump into a heavy-duty outdoor-rated cord if it's a plug-in pump.

A standby generator solves the "nobody's home" problem, but at standby prices.

What to skip

• Car batteries. Basement Watchdog says standby batteries outlast automotive batteries in this job.
• A backup with no alarm. Angi recommends pairing any backup with a water alarm.
• Water-powered backups on a well. They only run on municipal water.
• Setting the backup pump on dirt. Basement Watchdog says not to set the pump directly on clay, earth or sand; use bricks, blocks or a sump foot.

Installing a battery backup

Angi calls the job complicated and says most homeowners are better off hiring it out; if you DIY, set aside at least a day and check that a self-install won't void the warranty. Installed projects run $640 to $2,000, averaging $1,220, with labor at $45 to $200 an hour. The work is plumbing (a tee or second discharge, a check valve), setting the pump and float, and mounting the controller and battery above flood level. Basement Watchdog's preferred setup is a direct discharge to the outside of the building.

A plumber or a waterproofing contractor usually does it. If you need a new outlet near the pit, that part is an electrician's.