Sump Pump Battery Backup: Dedicated Pump or Power Station?

Two kinds of sump pump backup

People mix them up, but they solve the problem differently:

1. A dedicated battery backup pump. A second, 12 V pump usually sits in the pit above your main pump, with its own float, charger, battery and alarm. When the water rises past the main pump’s level, it starts by itself. It works during a power failure and also if the main pump itself fails.
2. A power station for your existing pump. A large battery with 120 V outlets runs the pump you already have. Plugged into the wall, some stations switch to battery on their own when the power cuts. It does nothing if the main pump itself breaks.

A third family, a battery and inverter backup system made for a 120 V pump, exists too; we have not added one to our catalogue yet.

Dedicated backup pumps compared

Flow at the same lift, 10 feet, is the fairest comparison. All four makers sell the pump without the battery.

*Maker claims; “at 10 %” means the pump runs 10 % of the time. Wi-Fi extra: a module sold separately.

What to look at before you buy:

• Battery size. Zoeller recommends a 90 Ah or larger deep-cycle battery, and no gel or car batteries ¹⁶. Superior asks for at least 40 Ah and says to avoid car batteries ¹⁸. Wayne recommends a 75 Ah AGM and says not to wire batteries in parallel ¹⁷. Basement Watchdog lets you link two batteries with a cable sold separately ².
• Alerts when you are away. Only the Zoeller has Wi-Fi built in ¹⁵.
• Runtime claims are not comparable. Zoeller and Basement Watchdog assume the pump runs 10 % of the time ^2,15. In a storm your pump may run far more.
• Pit size. Zoeller recommends at least 18 × 22 inches ¹⁹.
• CO alarms. Superior notes that any backup system with a lead-acid battery gives off gases while charging that can set off a false CO alarm. Place the battery as far from the detector as you can, never move the detector, and if it sounds, act for your safety first ¹⁸.

Running your existing pump on a power station

This works if your pump plugs into an outlet. Three stations from our catalogue, with runtimes for a 1/3 HP pump rated about 600 VA ³:

How we got these: capacity × 85 % ^5,6 ÷ (pump power + what the station uses on its own: 20 W published for the Apex 300 ¹², assumed for the others). At 10 % of the time, the pump averages 60 W. Small average loads can do worse than 85 % ⁶.

The trap: energy-saving modes. A sump pump can sit idle for hours. The Apex 300’s ECO mode, on by default, cuts the AC output after 4 h at 10 W or less ¹²; the Jackery’s Energy Saving Mode turns the outputs off after 12 h under 25 W ¹¹. When the water comes back, the pump would get no power. Turn these modes off: press the ECO button on the Apex ¹², or hold the Jackery’s AC and main power buttons for more than 3 seconds ¹¹. For the Anker, the user guide gives a default standby time of 12 hours, adjustable in the Anker app ¹⁰: set the longest time and test that the station stays on while the pump is idle.

Automatic switchover. If the station stays plugged into the wall with the pump plugged into it, it takes over during an outage: within 10 ms for the Anker ¹⁰ and the Jackery ¹¹, 20 ms for the Apex 300 at 120 V ¹². Jackery limits output to 1,440 W in this mode until the outage ¹¹. That is above the Liberty 1/3 HP pump’s 8 A start rating, about 920 VA ³, but check your own pump’s start current. Set the Apex 300’s UPS mode in the BLUETTI app ¹², and test the switchover by unplugging the station from the wall before the storm, as Jackery advises ¹¹.

How many watts a sump pump uses

The rating plate gives amps. Multiply by the voltage for the maximum:

• 1/3 HP (Liberty 250 series): 5.2 A running, 8 A locked rotor at start, 115 V ³: about 600 and 920 VA.
• 1/2 HP (Liberty 280 series): 8.0 A at 115 V ¹³: about 920 VA.

The power a motor actually uses in watts is a little lower than amps × volts, so these figures leave a margin. A motor also draws about three times its running current for a moment as it starts ²⁰: size the station’s surge rating for that. More detail in how many watts a sump pump uses.

How long a sump pump can go without power

It cannot pump at all, so the real question is how fast your pit fills. During the next heavy rain, time how often the pump starts. If it runs every few minutes, a power cut floods the pit within minutes, and a backup must start on its own. If it runs once an hour, a power station you plug in by hand may be enough.

Well pumps are different

A well pump is often 230 V. Franklin’s 4-inch well-pump motors come in 230 V from 1/3 to 5 hp, and in 115 V only from 1/3 to 1/2 hp ⁴. A deep-well pump is listed at 250 to 1,100 W ²⁰.

• A 115 V pump can run on a 120 V station, through a connection made by an electrician if it is wired in.
• A 230 V pump needs a 240 V source. Among our stations, the Apex 300 has a 120/240 V output switch ¹²; the Jackery needs a second unit for 240 V ¹¹. We could not verify the starting power of well pumps, so ask an electrician to size it.

If your well pump has no plug and is wired into the house, the connection is a job for a qualified electrician (see the safety note above). For other appliances, add up your list with the power station calculator. Our method is on the how we research page.