How Long Does a Backup Sump Pump Battery Last?

Before you buy a battery-powered backup sump pump, consider how long it will run during a severe rainstorm.

We have talked with hundreds of homeowners over the years who have had their basements unexpectedly flood due to a failed battery backup sump pump system. More often than not, the culprit is a dead battery. So before you invest in a backup sump pump system, it’s important to understand exactly how long the battery in your system will last and consider alternative backup sump pump options, such as a water-powered backup sump pump.

Your backup sump pump is the last line of defense against basement flooding when there is a power outage or your primary sump pump fails, so it’s important that it protects your basement in an emergency (see our article, Why You Need a Backup Sump Pump).

Run-time of a new fully-charged battery

As a general rule of thumb, during a power outage most new fully-charged batteries will last roughly 5-7 hours of continuous pumping and roughly 1-3 days of non-continuous pumping depending on the frequency. The longer the pump runs, the less power it has. This decline in battery power continues until the pump is completely overwhelmed by the water flowing into the sump pit and your basement floods.

backup sump pump battery
Backup sump pump battery

However, not all batteries have the same power capacity. Different batteries have different AH (ampere-hour) ratings, which affect how long it will run. North Dakota State University ran tests in their lab on lead-acid batteries rated at 40, 75, and 84 ampere-hours. They found the 40 AH battery lasted less than 4 hours, while the highest rated battery lasted around 7 hours.

Not only that, but the more powerful the pump, the shorter the run-time. Generally, backup pumps are either 1/4 HP or 1/3 HP. A 1/4 HP pump will have a lower current draw from the battery, maximizing the battery life. A more powerful 1/3 HP pump may pump faster, but it will also drain the battery quicker. Often times battery backup manufacturers will recommend a more expensive battery to accompany their relatively more powerful pumps.

Water-Powered Backup Sump Pump Installation
Water-powered backup sump pump installation

Because battery backup sump pumps have a limited life-span during a power outage, an alternative backup solution is the Water Commander water-powered sump pump. This system runs using your home’s municipal water pressure (see How Does it Work), so no batteries or electricity in any form is used. Water Commander’s pumping rates can exceed the pumping rates of standard battery backup pumps, but will maintain this pumping capacity for as long as it’s needed. It will not run out of power like battery backups.

Battery run-time decreases as it ages

However, these run times are the best case scenario. Backup sump pump systems can be several years old and still in use, which means the battery will likely perform below its optimal level. Many homeowners have found out the hard way that as a battery ages, its capacity to hold a charge also decreases. If your battery when new could run for around 7 hours continuously, after time passes it may only run for 2-3 hours or even less before losing power. Often times homeowners assume their battery has a charge, but don’t realize it is close to dying and only find out after their basement has flooded.

In wet-cell batteries, the most common type of lead-acid batteries used with sump pumps, this often happens because the lead plates within the battery become corroded over time and lose their ability to hold a charge.

As a battery ages, there will be a decrease in voltage which will effectively means there is less power and the battery will fail sooner. If you own a multimeter (also known as a volt-ohm meter or VOM meter), you can measure the voltage between the positive and negative terminal on the battery. If it is less than 12.1 volts, this is a sign the battery is aging and could fail prematurely during a rain storm.

Other causes of premature battery failure

There are a number of other factors that could negatively affect battery life. If a battery is exposed to extreme temperatures, this can affect its life. It’s also a good idea to keep the battery in a dry area. If it is exposed to water or excessive humidity, this will cause the battery to corrode quicker and lead to failures.

Consider Water Commander, the water-powered backup sump pump

Water Commander™ Water-Powered Backup Sump Pump
Water Commander backup sump pump

If you don’t already have one, seriously consider Water Commander™ water-powered backup sump pump instead. Unlike battery backups, Water Commander™ will never lose power and maintains the same high pumping rates regardless of the pumps age or how long it has been pumping. (See our Advantages page)

Not only that, you don’t have to worry about spending hundreds of dollars replacing the battery every several years. You can just test the pump to ensure proper working order by temporarily unplugging the primary electric pump or simply lifting the float switch by hand.

If you want to learn more about the Water Commander™, check out the rest of our website. If you have any questions, please reach out to us and we’ll help you out.

Live demonstration of a water-powered backup sump pump.

Looking for a quality backup sump pump?

Water Commander™ is the best backup sump pump system available on the market today. It’s non-electric, can out-pump your electric sump pump, and will run at full power for years to come.

It is more reliable than battery backups and is the perfect solution for homes with municipal water.

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