Sump pump battery backup cost

A sump pump battery backup costs $350 to $1,800 installed, typically around $900. That is a second, battery-driven pump set in the existing pit, with its own float, check valve, charger and controller, piped into the discharge.

What moves the price is how much water the backup has to handle and how long it has to keep going. A small backup with one battery protects a basement that takes water a few times a year. A basement that runs its pump every few minutes in a storm needs a bigger pump, more battery and a controller that tells you what it is doing.

What it costs

The battery itself is a consumable. Whatever the system costs on day one, budget for a replacement battery every few years, because the system is only as good as the battery in it on the night it is needed.

What runtime really means in an outage

Backup systems are sold on runtime, and the number on the box is rarely the number you get. Three things decide it.

How much charge the battery holds. Deep-cycle batteries are rated in amp-hours. A larger battery, or two wired together, holds more. A lead-acid battery should not be fully drained, and its usable capacity falls every year it ages.

How much the pump draws while running. A 12 volt backup pump draws a steady current while it runs. Divide usable amp-hours by that current and you get hours of continuous pumping, which on a typical single battery is a matter of hours, not days.

How often the pump runs. This is the number that matters most, and it belongs to your basement. A pump that runs ten seconds every ten minutes uses a small fraction of its continuous runtime per hour. A pump that runs ten seconds of every minute uses most of it.

The way to estimate it is to time your primary pump in a heavy rain: how long each cycle lasts and how long between cycles. If it cycles constantly during storms, one battery will not get through a long outage, and a second battery, a larger pump or a generator belongs in the plan.

Be aware too that most 12 volt backup pumps move noticeably less water than the primary they back up, and their output falls as the lift to the discharge rises. A backup is built to keep up with a normal storm until power returns, not to replace the primary for days.

Battery backup or water-powered backup

Battery backup works on any house, including one on a well. Its weakness is the battery, which loses capacity with age and fails quietly if nobody checks it.

Water-powered backup uses municipal water pressure to drive an ejector that pulls water from the pit. It needs no battery and runs as long as the city water does. It uses a lot of clean water to move pit water, it needs adequate pressure to do its job, it needs a backflow preventer, some jurisdictions restrict it, and it does not work on a well. It is priced by the installer and depends heavily on how far the water line is from the pit.

A combination unit puts a primary and a battery backup on one factory-built assembly, which helps in a narrow pit where two separate pumps and floats would foul each other.

A standby generator at $7,000 to $20,000 covers the sump with the rest of the house. It is rarely bought for the sump alone, but a house that already has one may only need the primary pump on a protected circuit.

For most houses on city water a battery system is the default, and water-powered is worth pricing where outages tend to be long. The sump pump replacement guide covers choosing the primary pump itself.

Battery types and the replacement cycle

Flooded wet-cell batteries are the cheapest. They need their water level checked and topped up with distilled water, and they vent gas while charging, so they want a vented battery box and a spot away from open flame.

Sealed AGM batteries cost more and need no watering. They are the usual choice in a finished basement because they can be left alone.

Lithium batteries are offered on some newer systems. They cost more again, hold their capacity longer and weigh far less, and they need a charger built for them.

Most lead-acid batteries in this service last roughly three to five years. Write the installation date on the battery, and replace it on that schedule rather than when it fails a test, because the failure usually shows up during the storm.

Alarms and controllers

The controller is the difference between a backup you trust and one you hope works.

A self-test runs the backup pump briefly on a schedule to confirm it starts.

A battery alarm sounds when charge is low or the battery is failing.

A high-water alarm sounds when the water reaches a level the primary should have cleared. It is worth having even without a backup.

A remote alert sends a message to a phone when any of these trip. For a house that sits empty during travel, or a basement nobody walks through, it is the most useful feature on the list.

An alarm that sounds in an unfinished basement while everyone sleeps two floors up does little. Put the controller where it can be heard, or choose one that can alert remotely.

A worked example: an aging pump in a finished basement

A finished basement has a nine-year-old submersible pump and no backup. The owners replace the primary on their own schedule and add a battery backup on the same visit, so the plumber works in the pit once.

• New primary pump: $650 to $2,500
• Battery backup system: $350 to $1,800
• Total: $1,000 to $4,300

The low end is a basic pump, a basic backup and an easy pit. The high end is a cast iron primary, a larger backup with an extra battery and a remote-alert controller, and pit or discharge work that needed redoing. Doing both at once saves a second trip and makes sure the two pumps, floats and check valves are set up to work together.

Set that against an emergency visit during a flood, billed at $150 to $300 an hour, plus whatever the water reaches first in a finished room.

Questions to ask before you buy

• What is the backup pump's output at my actual lift to the discharge?
• What battery is included, how many amp-hours, and can a second be added?
• Does it share the primary's discharge line, and does each pump have its own check valve?
• Does the controller self-test, and how does it alert me?
• Will both pumps and their floats fit in my pit without catching on each other?

Frequently asked questions

How much does a sump pump battery backup cost installed?

$350 to $1,800 installed, typically about $900. Larger pumps, extra batteries, remote alerts and pit or discharge rework push it toward the top. The battery needs replacing every few years on top of that.

How long will a sump pump battery backup run?

It depends on battery capacity, pump draw and how often the pit fills. Continuous pumping on one battery lasts hours, but intermittent pumping in a normal storm stretches that much further. Timing your primary pump in a heavy rain is the best way to estimate it.

How often should a sump pump backup battery be replaced?

Roughly every three to five years for a lead-acid battery, sooner if the controller reports it weak. Write the installation date on it and replace it on schedule rather than waiting for it to fail.

Is a water-powered sump pump backup better than a battery?

It runs without a battery as long as city water pressure holds, which makes it strong in long outages. It uses a lot of water, needs a backflow preventer, may be restricted locally, and does not work on a well. A battery system works on any house but depends on a battery being kept in good condition.

Related guides

• Sump pump replacement cost — choosing the primary pump the backup protects
• Sump pump installation cost — adding a pit where there is none
• Wet basement repair cost — the fixes that reduce how often either pump runs
• Whole-house generator cost — covering the sump along with the rest of the house