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Everything to Know About Sump Pump Battery Backups

Updated: Dec. 08, 2022

A dead pump can lead to disaster. Here's how to avoid trouble

sump pumpsFamily Handyman

A good sump pump installation should include a backup system for breakdowns and power outages. Learn the pros and cons of four pump backup methods.

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Can you count on your sump pump?

A sump pump is one of the most important (and most ignored) disaster prevention devices in a home. When this simple system fails, the results can be catastrophic, leading to thousands of dollars in damage, daily disruptions caused by major repair work and higher insurance premiums for years to come. So spending some time and money on avoiding failure makes a lot of sense. Here find out how long sump pumps last.

Some homeowners keep a replacement pump on hand in case their pump dies. That’s a good idea (home centers often sell out of pumps during storms or floods). But having a replacement handy won’t help you if you’re on vacation during a power outage or if your pump dies while you’re slumbering through a stormy night. That’s the beauty of sump pump backup systems: No matter what the reason for the pump failure, a backup system will save the day. In this article we’ll show you the options.

What causes primary pumps to fail?

The most common reason for pump failure is a power outage, not some problem with the pump itself. Common events besides power outages can also cut off the supply of electricity. For example, lightning can trip GFCI outlets, or someone can unplug the pump and forget to plug it back in.

Assuming the power stays on, sometimes the pump itself fails. Many inexpensive sump pumps are simply too small to handle the flow from a major downpour or rapid snowmelt. And because inexpensive pumps are built with less durable materials, they lose pumping efficiency. So the pump runs more often and burns out early. Or the motor runs but the pump doesn’t eject water.

Float switches are also a frequent cause of pump failure. “Wide angle” tethered float switches, the kind that free-float around the sump basket, are the biggest troublemakers. They swirl around the sump basket, making them far more likely to get trapped against the pump, discharge pipe or power cord. Once trapped, they can’t switch on the pump. Inexpensive switches can also simply wear out or cause motor burnout.

Sizing a Pump

Whether you’re buying a replacement pump or a backup system, you’ll have to determine the pump capacity. Here’s how: Disconnect your existing pump, pull it out of the basket, and check the GPH rating on the label or check the pump’s specifications on the manufacturer’s Web site. Buy a new pump with at least that much capacity. If your existing pump sometimes can’t keep up with the incoming water, select a model with a higher GPH rating.

Battery backup sump pump systems

sump pump backup battery system components

Battery system components

A sump pump battery backup consists of a battery, a battery-powered pump, a charger and additional piping.

Manufacturers of battery backup systems usually sell three models: good, better and best, with “best” costing three times as much as “good”. The “best” units come with a larger battery and a more sophisticated battery charger. The larger battery gives you a longer run-time, and the better charger prolongs the life of the battery.

So how long will a battery backup system keep your basement dry? That depends on how much water is entering your sump basket (which determines how often the pump will run). Here’s an example: one manufacturer’s system comes with a 40-amp/hour battery that’s projected to last up to 53 hours (pumping at the rate of 2,300 GPH once every five minutes). But, if you have serious water problems such that the pump runs once a minute, that same battery will last only 12 hours. That’s hardly enough battery capacity to get you through an extended power outage. In that case, buy a system with a larger battery, or a system with a charger large enough to keep two batteries fully charged.

If you have minor seepage and rarely experience power outages, you’re probably safe buying a less expensive battery backup system. Then again, that savings could cost you big-time if just one 100-year storm knocks out your power and turns a sump trickle into a flood.

Advantages of battery backup systems

    • Simple installation—connect to existing discharge pipe or run a separate pipe
    • Unlike water-powered systems, battery backup systems work when there’s no water supply


  • Battery may run down before power comes back on
  • Battery water levels must be checked every few months
  • Battery terminals must be cleaned twice a year
  • Battery must be replaced every five years (and costs about $100).

Figure A: Battery Backup Pump

If the primary pump fails, the battery-powered pump takes over and ejects water. A maintainer keeps the battery at full charge.

Water-powered backup

Above-sump backup pump

Above-sump backup pump

An above-sump backup unit has less chance of drinking water contamination and uses a less expensive type of backflow preventer.

In-sump backup pump

In-sump backup pump

An in-sump water-powered pump always has water in it, and requires a more expensive type of back-flow preventer.

A water-powered backup pump uses water pressure to siphon water out of your sump. Most use 1 gallon of city water for every 2 gallons of sump water they remove. So a pump that’s capable of removing 1,500 GPH will use 750 GPH of city water. And that’s created a lot of controversy. In fact, a few municipalities prohibit their use due to already severe water shortages. So check with local ordinances before buying a water-powered sump pump. In an area with high water costs, the water bill can run as high as $170 a day. But keep that in perspective. If your power goes out for a couple of days, you’d happily pay a $300 water bill to avoid a flood.

Water-powered pumps require at least 40 psi and a 3/4-in. feed line to achieve maximum pumping rates. And they require a separate drain line and some type of backflow prevention to prevent cross-contamination with potable water.

Water-powered pumps come in two styles: in-sump and above-sump. An in-sump pump (one choice is the Liberty No. SJ10 SumpJet pump, available through our affiliation with is always immersed in drain water, which raises the risk that drain water could contaminate the drinking water supply. To prevent that, most local codes require the installation of an expensive reduced pressure zone (RPZ) backflow prevention valve. RPZ valves must be professionally installed and tested annually by a licensed plumber. That adds an annual cost to the system. So check with your local building inspection department before you buy an in-sump system.

An above-sump unit mounts well above the sump, which reduces the risk of drinking water contamination (one choice is the Basepump RB750-EZ; sold at Therefore, many plumbing inspectors require only a less expensive atmospheric vacuum breaker (AVB).


    • No limit to run-time; works as long as you have water pressure
    • No battery replacement costs
    • No routine maintenance


  • If you have a well, this setup won’t work during a power outage
  • More difficult installation because it requires a new water line, backflow preventer and new drain line
  • Annual fee for RPZ valve testing (if required by local code)
  • May be expensive to run in areas with high water costs

Figure B: Above-Sump Water-Powered Pump

This pump operates like an in-sump unit, using city water to pump sump water. Both kinds of water powered systems require a separate discharge line.

Figure C: In-Sump Water Powered Backup

When the primary pump fails, a water-powered pump uses city water pressure to siphon water out of the sump. With an in-sump version, your local inspector may require an RPZ valve to prevent contamination of drinking water.

Generator-powered sump pump

During a power outage, a generator can pay for itself in a dozen ways. One of those ways is powering a sump pump. A typical sump pump draws about 9 amps, so it won’t add much load to the generator. But a generator isn’t a perfect substitute for a backup system. A battery- or water-powered system kicks in automatically, whether you’re home or not and no matter what the failure. A portable generator works only if you’re around to connect it. And a generator (standby or portable) won’t help if your primary sump pump is kaput.

Figure D: Power Pump With a Portable Generator

Run a heavy-duty extension cord from the sump pump to the generator.

Know when your pump is dead

Too often, homeowners don’t discover a sump pump failure until they see the damage. But there are ways to avoid that:

If you buy a new AC sump pump run by a controller, it’ll have some type of alarm to let you know if the pump fails or the power goes out. The same holds true for most new battery-powered systems.

  • Local Alarm. Detects water at the top of the sump basket using either a probe or a float and sounds an audible alarm (such as the BWD-HWA Basement Watchdog Water Sensor and Alarm; available through our affiliation with Local alarms are great if someone is home at the time of the failure.
  • Verbal Message Via Landline. Detects water at the sump and dials a preprogrammed phone number and plays a recorded message (one choice is the Control Products WA-700 WaterAlarm Dialer; from Also sounds an audible alarm. Must have a landline.
  • Text Messaging. Detects water at the sump and sends a text to three different cell phones. Search “high water text notification” for companies that provide this service.

How to Buy a Primary Sump Pump

Home centers sell a confusing array of sump pumps that range from $50 to $250. But don’t despair. We’ve reviewed all the specs, talked to the engineers and boiled it down to five simple buying tips:

1. Horsepower means nothing. It’s the pumping volume in gallons per hour (GPH) that counts. Check the capacity of your current pump. If your current pump keeps up with the flow during the heaviest rainstorms, buy that capacity again. If not, buy a pump with a higher GPH rating. To find your current pump’s rating, locate its make and model number on the label and find the specs on the manufacturer’s Web site.

2. Check the “head” on the manufacturer’s GPH rating. Head is the height that water has to be lifted from the pump to the horizontal discharge pipe. More height means harder work for the pump. The GPH rating on most good-quality pumps includes the head (typically 10 ft.). But some manufacturers rate pump capacity without head (“3200 GPH at 0 head” for example). That gives an unrealistic—and misleading—estimate of pump capacity.

3. Spend the money to get a quality sump pump. Look for a caged or vertical float switch, a motor with a UL and a CSA rating, and a pump made with a stainless steel, cast aluminum or cast iron impeller and pump body. Avoid pumps made from epoxy-coated parts. Find out the cost of a sump pump.

4. Buy an energy-efficient pump. Once you find a pump with the correct GPH rating, look for a model that consumes the fewest amps. This isn’t about saving electricity; high-amp pumps run hotter and burn out the float switch faster.

5. If your sump accumulates gravel or sand, buy a “top suction” pump that’s “solid passing” to prevent a stall/burnout caused by trapped gravel. Or raise a “bottom suction”-style pump on a few bricks to keep it off the bottom of the sump.

While you’re at the home center, buy a new male fitting to fit the pump outlet; pipe primer and cement; a new check valve and rubber couplers.