Prices checked 11 October 2026 · page dated 11 October 2026 · not a hands-on test · no flood guarantee
Battery backup for a sump pump: size for the start, keep a second line of defense
A sump pump is not like a well pump. Most are 120 V, sit in a pit in the basement, and run in short bursts: the float rises, the motor starts, the pit empties, it stops, and it does that again a few minutes later in a heavy rain. The number that decides whether a battery works is the start surge on every cycle, not the watt-hours.
Edited by K Singh. contact@outageshield.com. Manufacturer pages and dated list prices only. No invented homeowner stories. No test lab. Not a wiring diagram.
This page is the decision gate for one pump: label → start surge → cords or inlet + interlock → a second line of defense that does not depend on any battery. Well pumps (240 V, a different job) are on the soft-start well pump guide. Keeping a gas furnace on the same circuit plan is on gas furnace blower. House connection detail is on generator inlet & interlock.
Three-gate summary
- Label — volts, HP and amps on the pump label or in the manual.
- Start surge — the inverter must start the motor on every cycle. Extra batteries add hours, not starting current.
- Path — cords if the pump plugs into a receptacle; inlet + interlock if it should run with the furnace and fridge. Never backfeed.
1. Who this is for
You have a basement or crawlspace sump with an electric primary pump, and outages in your area tend to come with heavy rain or snowmelt — exactly when the pump runs most. You want to know what size of battery honestly keeps it running, and what happens if the battery runs out.
This page does not cover sewage ejector pumps, 240 V pumps, or commercial duplex systems. If your pump label says 230 V, stop and treat it as a different job.
2. Gate 1 — Read the label
Unplug the pump (or turn off its circuit) before you reach into the pit. The label is usually on the motor housing or the cord tag; the manual lists the same numbers.
| Marking | What it means for backup |
|---|---|
| Volts / Hz | Most residential sump pumps read 115–120 V, 60 Hz. |
| HP | 1/3 HP and 1/2 HP are the common sizes; 3/4 and 1 HP exist for high-inflow pits. |
| Amps (FLA) | Running amps. Amps × 120 ≈ running watts. |
| Plug | A cord-and-plug pump points to the cord path. A piggyback float plug (the pump plugs into the float switch’s plug) is still cord-and-plug. |
| Pump size | Ballpark running draw (not your pump) | Ballpark start surge |
|---|---|---|
| 1/3 HP | Roughly 400–800 W | Often 2–3× running for a fraction of a second |
| 1/2 HP | Roughly 600–1,050 W | Often 2–3× running |
| 3/4–1 HP | Roughly 900–1,500 W | Can approach 3–4 kW at start |
These are planning ranges. Your label governs, and the only real check is to run the pump on the battery: fill the pit with a hose on a dry afternoon and watch it start several times in a row.
3. Gate 2 — Start surge, every cycle
A well pump starts a few times an hour. A sump pump in a storm can start every few minutes, for hours. Each start pulls the surge from the inverter.
- Pick a pure-sine inverter whose listed surge rating clears your pump’s start with room to spare, and whose continuous rating clears the running watts plus anything else on the same battery.
- Batteries add hours, not starting current. A second pack lets the same inverter run longer; it does not help a too-small inverter start a 3/4 HP pump.
- If the pump trips the battery’s overload on start, stop. Do not swap in a longer extension cord or an adapter. The fix is a bigger inverter, or a pump choice made with a plumber.
Watt-hours, honestly: a 1/3 HP pump drawing ~600 W that runs 15 seconds every 5 minutes averages about 30 W (~0.03 kWh an hour); the same pump running a third of every hour in a hard storm averages ~200 W (~0.2 kWh an hour). Inflow decides which, and nobody can predict it for your pit. Put your numbers in the runtime calculator.
| Battery capacity | Example units | Pump-only hours at ~200 W average (hard storm) |
|---|---|---|
| 2,048 Wh | Anker SOLIX C2000 Gen 2, BLUETTI AC200L | ~8.7 h |
| 3,840 Wh | Anker SOLIX F3800 Plus | ~16 h |
| 4,096 Wh | EcoFlow DELTA Pro 3 | ~17 h |
| 7,680 Wh | F3800 Plus + one BP3800 | ~33 h |
We assume ~85% of rated capacity is usable. This is planning math, not a measured result, and every other kept load — fridge, furnace, router, lights — comes out of the same battery. We do not promise that any battery runs a sump pump through a whole storm.
4. Gate 3 — Pick the path
| Path | When it fits | What it takes | Honest limit |
|---|---|---|---|
| Cords to the pump | The pump plugs into a receptacle and the pump is the main thing you need | A 120 V pure-sine portable with enough surge; plug the pump (or its piggyback float) straight in | The battery sits in a basement that may get wet — keep it off the floor and away from the pit |
| Inlet + interlock | The sump should run alongside the furnace, fridge, router and lights | Listed inlet, panel-matched interlock or transfer switch, licensed electrician, permit where required | Manual flip; the battery must cover every kept circuit at once. Detail: inlet & interlock. |
Never backfeed through a dryer or wall receptacle. Never feed a panel with the main breaker on unless a listed interlock or transfer device makes that impossible. An inlet, interlock or transfer switch is a licensed electrician’s job, with a permit where required. Overview: how to connect a portable.
Most sump pumps plug into a receptacle near the pit, which is often a GFCI. On backup power through cords, plug directly into the battery’s outlet. If the pump trips a GFCI on the grid, have that fixed before an outage, not during one.
5. The part a battery cannot do
If the pack is dead — the outage ran long, the battery was never charged, or water reached it — the primary pump stops and the basement floods. The second line of defense should not depend on the same battery.
| Backup type | How it works | What to know |
|---|---|---|
| Water-powered (venturi) backup pump | Uses city water pressure to pull water from the pit; no electricity | Needs municipal water pressure (not a private well, which loses pressure in an outage); uses a lot of water; plumber install and a backflow preventer where code requires |
| Dedicated DC battery backup pump | A second pump with its own deep-cycle battery and charger | Its own battery and alarm; still finite, so check its battery yearly |
| High-water alarm | Sounds when the pit rises past normal | Cheap and battery-powered; tells you the plan failed while there is still time |
A portable power station is a good way to keep the primary pump running through an ordinary outage. Pair it with one of the above if a flooded basement would be expensive.
6. Multi-day outages
If an outage can run past two days, rain is likely to keep falling, solar recharge is weak under storm cloud, and the sump shares the battery with the fridge and furnace. The honest answers are more kWh, a generator to recharge, or both. Duration math across all three is on generator vs battery vs hybrid for a 2–4 day outage; cold-storm planning is on ice storm 2-day backup, and the order things fail is on what dies first.
7. Shop-ready pointers (prices checked 11 October 2026)
| Unit | Fits which path | Price snapshot |
|---|---|---|
| Anker SOLIX C2000 Gen 2 — 2,048 Wh / 2,400 W, 120 V | Cords, 1/3–1/2 HP pump (check surge against the label) | $899.99 Halloween sale / $1,199.99 list (checked 26 Oct 2026, sale ends 1 Nov 2026) |
| BLUETTI AC200L — 2,048 Wh / 2,400 W, 120 V | Cords, 1/3–1/2 HP pump (check surge against the label) | $899 sale / $1,599 list (BLUETTI US) |
| Anker SOLIX F3800 Plus — 3,840 Wh / 6,000 W, 120/240 V | Inlet + interlock with other must-run loads, or larger pumps | $2,399.99 Halloween sale / $2,999.99 list (checked 26 Oct 2026, sale ends 1 Nov 2026); BP3800 expansion battery $1,799.99 Halloween sale / $1,999.99 list (checked 26 Oct 2026, sale ends 1 Nov 2026) |
| EcoFlow DELTA Pro 3 — 4,096 Wh / 4 kW | Inlet, or EcoFlow’s manual transfer switch kit | $2,799 sale / $3,299 list; transfer switch $399 (EcoFlow US) |
Shop-ready sources after the label check. Confirm checkout prices — they move. A sump alone does not justify a whole-home install; ranked picks are on best batteries for frequent outages without solar.
View C2000 Gen 2 on Anker View AC200L on Bluetti View F3800 Plus on Anker View BP3800 on Anker View DELTA Pro 3 on EcoFlow View transfer kit on EcoFlow8. How this connects
- Decision (this page) — label, start surge, path, second line of defense.
- House connection — how to connect; middle path — inlet & interlock.
- Other must-run loads — gas furnace blower; well pumps — soft-start well pump; oxygen concentrator (loads differ).
- Duration — ice storm 2-day backup; generator vs battery vs hybrid; sequence — what dies first; charge the night before.
- Your numbers — runtime calculator; keep list — checklist.
FAQ
Sources (checked 11 October 2026)
- Anker SOLIX US product pages (ankersolix.com/products/c2000-gen2, /f3800-plus, /bp3800-expansion-battery) — C2000 Gen 2 $899.99 Halloween sale / $1,199.99 list (checked 26 Oct 2026, sale ends 1 Nov 2026); F3800 Plus $2,399.99 Halloween sale / $2,999.99 list (checked 26 Oct 2026, sale ends 1 Nov 2026); BP3800 $1,799.99 Halloween sale / $1,999.99 list (checked 26 Oct 2026, sale ends 1 Nov 2026)
- BLUETTI US AC200L product page (bluettipower.com/products/ac200l) — $899 sale / $1,599 list (checked 11 October 2026)
- EcoFlow US product pages (us.ecoflow.com/products/delta-pro-3-portable-power-station, /transfer-switch) — DELTA Pro 3 $2,799 sale / $3,299 list; transfer switch $399 (checked 11 October 2026)
- Pump draws and start surge are ballpark planning ranges; your pump label governs
Next step: read the pump label, then decide cords vs inlet + interlock — and pick a backup pump or alarm that does not need the battery.
Ice storm 2-day Inlet & interlock Runtime calculator Find my backupEditor: K Singh. Prices checked 11 October 2026. Page dated 11 October 2026. Not a hands-on test. Not electrical or plumbing advice for your jurisdiction. We do not guarantee that any battery will keep your basement dry.