The best battery backup for an existing sump pump depends on whether you want to add a separate backup pump, power your current AC sump pump during outages, or replace the battery component in a compatible backup setup. For most homeowners, the right choice comes down to the pump you already have, the sump pit layout, the amount of water you need to move, and how long outages usually last in your area.
This guide compares three approved options for existing sump pump setups: an add-on battery backup pump, an inverter-style backup system, and a deep cycle AGM battery for compatible backup systems. Each product fits a different type of upgrade, so the best choice depends on whether your existing pump needs support, backup pumping, or battery storage.
Quick Picks
- Best overall for adding backup to an existing sump pump: WAYNE ESP25 / ESP25N Battery Backup Sump Pump, because it gives homeowners a dedicated backup pump instead of relying only on the existing primary pump.
- Best for powering a compatible existing AC sump pump: Pump Sentry 822PS Sump Pump Backup System, because it is designed for inverter-style backup power rather than adding a separate pump.
- Best supporting battery option: Renogy Deep Cycle AGM 12 Volt 100Ah Battery, because it can support compatible backup systems that require a separate deep cycle battery.
WAYNE ESP25 / ESP25N Battery Backup Sump Pump
An add-on battery backup sump pump for homeowners who want outage protection alongside an existing primary sump pump.
The WAYNE ESP25 / ESP25N Battery Backup Sump Pump is the strongest fit for homeowners who already have a working primary sump pump but want a dedicated backup pump for outages. It is especially relevant if the existing pump works well during normal conditions, but you are worried about power loss during storms.
Best for: Homeowners who want to add a separate battery backup pump to an existing sump pit.
Main advantage: It gives you a second pumping path if the primary pump cannot run during a power outage.
Main limitation: It still needs proper installation, battery support, discharge planning, float switch placement, and enough room in the sump pit.
Pump Sentry 822PS Sump Pump Backup System
An inverter-style sump pump backup system for powering a compatible existing AC sump pump during outages.
The Pump Sentry 822PS Sump Pump Backup System is a better fit if you want to keep using your existing AC sump pump during an outage instead of adding a separate backup pump. It is an inverter-style system, so the main question is whether your current pump is compatible with the backup unit and battery setup.
Best for: Homeowners who want battery backup power for a compatible existing sump pump.
Main advantage: It can let the existing pump continue working when utility power fails, provided the pump and system are properly matched.
Main limitation: It depends heavily on compatibility, pump startup demand, battery capacity, and correct setup.
Renogy Deep Cycle AGM 12 Volt 100Ah Battery
A deep cycle AGM battery option for compatible sump pump backup systems that require separate battery storage.
The Renogy Deep Cycle AGM 12 Volt 100Ah Battery is a supporting product, not a complete sump pump backup solution. It is included here because some existing sump pump backup systems need a separate deep cycle battery to store power for outages.
Best for: Buyers who need a compatible battery for an existing sump pump backup system or inverter-style setup.
Main advantage: It provides stored energy for compatible backup equipment where a separate battery is required.
Main limitation: It does not move water by itself and should only be used when the backup system’s battery requirements match.
What to Look For
- Decide whether you want a backup pump or backup power. An add-on pump gives you a separate pumping path, while an inverter system powers a compatible existing pump.
- Check sump pit space. A backup pump needs room for the pump, float switch, piping, and proper water movement.
- Confirm battery requirements. Some systems need a separate battery, and not every battery is suitable for every backup setup.
- Match the backup to your water volume. A home with heavy water inflow during storms may need stronger backup planning than a basement with occasional seepage.
- Look at discharge routing. Backup systems still need a safe way to move water away from the home.
- Plan for maintenance and testing. A backup system should be tested before storm season, not discovered during an outage.
Final Recommendation
The best overall battery backup for an existing sump pump on this page is the WAYNE ESP25 / ESP25N Battery Backup Sump Pump. It is the clearest fit for homeowners who already have a primary sump pump and want a dedicated backup pump for outage protection.
The Pump Sentry 822PS Sump Pump Backup System is the better choice if your existing AC sump pump is compatible and you prefer an inverter-style backup power system instead of adding another pump.
The Renogy Deep Cycle AGM 12 Volt 100Ah Battery is useful as a supporting battery for compatible systems, but it should not be treated as a complete backup by itself. Avoid choosing only a battery if you still need a pump, controller, inverter, charger, or full backup system.