How to Install a Sump Pump Battery Backup
Updated March 2, 2026
Add a battery backup to your sump pump system so it keeps running during power outages -- when heavy rain makes flooding most likely.
Overview
Power goes out during heavy storms. Heavy storms are exactly when your sump pump works hardest. A battery backup sump pump sits in the same pit as your primary pump and activates automatically when the power fails or the primary pump cannot keep up. It runs on a 12V marine battery that provides 4-12 hours of pumping depending on battery size and water volume. Installing one is the difference between a dry basement and 6 inches of standing water after a storm knocks out power for 4 hours.
What You'll Need
Safety First
- Marine batteries produce hydrogen gas when charging. The sump pit area needs ventilation -- do not install in a sealed, enclosed space.
- Battery acid is corrosive. Wear gloves and safety glasses when handling the battery. If acid contacts skin, flush immediately with water.
- The battery charger must plug into a GFCI-protected outlet. Water and electricity are in close proximity at a sump pit.
Step-by-Step Instructions
- Choose the Right Backup System
Battery backup systems come as complete kits: a secondary pump, a charger/controller unit, a battery, and a float switch. Top brands: Wayne WSS30VN ($250-$350, includes pump and charger), Zoeller Aquanot 508 ($300-$400, higher capacity), and basement Watchdog BW4000 ($200-$300, good mid-range). Choose based on the GPH (gallons per hour) rating at your pit's lift height. A typical basement needs 2,000-3,000 GPH at 10-foot lift. Check the battery run time -- 4-8 hours is standard on a full charge.
Tip: The Wayne WSS30VN is the most popular residential backup. It includes a 1/2 HP AC primary pump AND a DC backup pump in one package. If your primary pump is aging, this combo unit replaces both at once. - Install the Backup Pump in the Pit
The backup pump sits alongside the primary pump in the same sump pit. Position it so the float switch activates at a level ABOVE the primary pump's float -- the backup only runs when the primary cannot keep up or has failed. Connect the backup pump's discharge pipe to the existing discharge line using a check valve and a tee fitting. Each pump needs its own check valve to prevent backflow from one pump into the other. The backup discharge can tee into the primary discharge above the check valves.
Tip: Do not set the backup float at the same level as the primary. The backup should be a secondary defense -- it activates only when water rises above the primary pump's normal shutoff point. This prevents unnecessary battery drain during normal operation. - Set Up the Battery and Charger
Place the marine deep-cycle battery ($80-$150) on a stable surface near the pit -- not in the pit (water damages the battery). A shelf, plastic crate, or battery tray works. Connect the battery cables to the charger/controller unit (red to positive, black to negative). Plug the charger into a GFCI outlet. The charger maintains the battery at full charge continuously, only drawing significant power when the battery needs topping off. Most chargers have LED indicators showing charge status.
Tip: Use a Group 27 or Group 31 deep-cycle marine battery -- not a car battery. Car batteries deliver high amperage for short bursts (starting an engine). Deep-cycle batteries deliver moderate amperage for extended periods (running a pump for hours). Car batteries fail quickly in backup pump applications. - Test the System
Fill the pit with a garden hose or buckets until the primary pump activates and pumps down. Then unplug the primary pump (simulating a power outage). Continue filling. The backup pump should activate when water reaches its float level. Verify: the backup pumps water out, the discharge does not leak at any connection, and the alarm sounds (most systems have an audible alarm when the backup activates). Plug the primary back in. Check the charger -- it should show the battery is charging or fully charged.
Tip: Test the backup system every 3 months. Pour a bucket of water into the pit with the primary unplugged. The backup should kick on within seconds. A backup that has not been tested in a year may have a dead battery when you need it most.
Pro Tips
- Replace the marine battery every 3-5 years regardless of whether it has been used. Batteries degrade even when maintained at full charge. A fresh battery costs $80-$150 -- cheap insurance against a flooded basement.
- Wi-Fi sump pump monitors ($30-$100, Basement Watchdog, PumpSpy) send alerts to your phone when the backup activates, when the battery is low, or when water reaches the alarm level. Essential if you travel or work away from home.
- A water-powered backup pump ($200-$400) uses municipal water pressure instead of a battery. It pumps 1 gallon of sump water for every 2 gallons of city water used. No battery to maintain, runs indefinitely during power outages. The tradeoff: it uses city water and does not work if you are on a well.
- The battery charger draws 1-3 amps continuously to maintain the battery. This adds $5-$15/year to your electric bill. The charger must stay plugged in at all times -- unplugging it to save electricity defeats the purpose.
- If your basement floods frequently or you live in a flood-prone area, consider a whole-house generator ($3,000-$10,000) that powers the primary pump, furnace, and other essentials during extended outages. A battery backup provides 4-12 hours; a generator provides days.
When to Call a Pro
You do not need a plumber for a battery backup installation. The pump, charger, and battery are all plug-and-play. Call a plumber if the sump pit is too small for a second pump (pit may need to be enlarged), if you want the backup discharge line routed separately from the primary (separate discharge prevents both pumps from failing if the primary discharge line freezes or clogs), or if you want a water-powered backup installed (requires connection to the municipal water supply).
Frequently Asked Questions
When should I call a plumber to install a sump pump battery backup?
You do not need a plumber for a battery backup installation. The pump, charger, and battery are all plug-and-play. Call a plumber if the sump pit is too small for a second pump (pit may need to be enlarged), if you want the backup discharge line routed separately from the primary (separate discharge prevents both pumps from failing if the primary discharge line freezes or clogs), or if you want a water-powered backup installed (requires connection to the municipal water supply).
What are some expert tips to install a sump pump battery backup?
Replace the marine battery every 3-5 years regardless of whether it has been used. Batteries degrade even when maintained at full charge. A fresh battery costs $80-$150 -- cheap insurance against a flooded basement. Wi-Fi sump pump monitors ($30-$100, Basement Watchdog, PumpSpy) send alerts to your phone when the backup activates, when the battery is low, or when water reaches the alarm level. Essential if you travel or work away from home. A water-powered backup pump ($200-$400) uses municipal water pressure instead of a battery. It pumps 1 gallon of sump water for every 2 gallons of city water used. No battery to maintain, runs indefinitely during power outages. The tradeoff: it uses city water and does not work if you are on a well. The battery charger draws 1-3 amps continuously to maintain the battery. This adds $5-$15/year to your electric bill. The charger must stay plugged in at all times -- unplugging it to save electricity defeats the purpose. If your basement floods frequently or you live in a flood-prone area, consider a whole-house generator ($3,000-$10,000) that powers the primary pump, furnace, and other essentials during extended outages. A battery backup provides 4-12 hours; a generator provides days.
What tools do I need to install a sump pump battery backup?
You will need: Battery backup sump pump kit ($150-$400, includes pump, charger, float switch, and hardware), Deep-cycle marine battery, Group 27 or 31 ($80-$150), PVC pipe, fittings, and check valve (for discharge connection -- some kits include these), PVC cement and primer (for permanent pipe connections), Adjustable wrench (for check valve and fitting connections).
When should I call a professional instead of doing this myself?
You do not need a plumber for a battery backup installation. The pump, charger, and battery are all plug-and-play. Call a plumber if the sump pit is too small for a second pump (pit may need to be enlarged), if you want the backup discharge line routed separately from the primary (separate discharge prevents both pumps from failing if the primary discharge line freezes or clogs), or if you want a water-powered backup installed (requires connection to the municipal water supply).
How difficult is this project?
This project is rated intermediate. It requires moderate DIY skill and the right tools.
How long does this take?
Plan for approximately 1 - 2 hours. First-timers may need extra time.
How much will this cost?
The estimated cost is $150 - $400 for the backup system. Costs vary by location and materials chosen.