By the makers’ figures: 40 hours for Basement Watchdog’s Big Dog CONNECT on one battery, up to 96 hours for its BWSP on two, and up to 10,000 gallons on one charge for a WAYNE ESP25n.
Which backup pump?
How many batteries?
Backup pump runtime
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The pumps and their batteries
Each backup pump’s flow at 10 feet and the battery it takes
Pump
Flow at 10 ft
Battery
Basement Watchdog Big Dog CONNECT (BWD12-120C)
2,200 gallons an hour
One or two BW-27AGM
Basement Watchdog BWSP
1,850 gallons an hour
One or two BW-27AGM
WAYNE ESP25n
1,500 gallons an hour
One 12 V AGM, up to group 27
Basement Watchdog’s hours assume a 10% duty cycle, and it says runtimes vary with water flow. WAYNE gives gallons on a charge instead of hours.
Which battery
Basement Watchdog says the Big Dog CONNECT takes maintenance-free AGM or wet-cell batteries, and its BW-27AGM needs no battery fluid added. It sells a cable, Model PJC, for a second battery, which it says doubles the runtime.
WAYNE says the ESP25n works most efficiently with AGM batteries, and its case holds one up to a group 27 size.
Safety
WAYNE warns that batteries can release dangerous hydrogen gas while charging, and says to keep the area around them well ventilated.
Have a plumber install a backup sump pump.
Common questions
How much current does a backup sump pump draw?
Basement Watchdog lists 20 amps for the Big Dog CONNECT's DC pump at 10 ft of total head, and 18 amps for the BWSP's.
Runtimes, flows and batteries come from Basement Watchdog’s product pages and WAYNE’s ESP25n page and manual, read on October 25, 2026. Checked against published data from Basement Watchdog and WAYNE.
See all 4 sources
Basement Watchdog, Big Dog CONNECT Battery Backup Sump Pump (product page and specification table, with the BWSP)
WAYNE, ESP25n Operating Instructions and Parts Manual (600005W-001-J, PDF)
Battery sizes come from battery makers' datasheets and device makers' own manuals and help pages. Check your device's manual or the old battery before you buy. If anyone may have swallowed a battery, call the National Battery Ingestion Hotline at 1-800-498-8666 or your poison center at 1-800-222-1222 straight away.