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Fix a battery backup that will not charge

We'll confirm power, check connections, test the battery, then replace it if needed.

Troubleshooting · Home maintenance
15–30 min
What you'll need
  • Multimeter (to test battery voltage)
  • Replacement battery (if needed)
Step 1 of 8

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Steps

Goal: Confirm power, check connections, test the battery, then replace if needed.

  • Check the battery backup unit. A red light, flashing light, or charge fault message indicates the battery is not charging.
  • Good: Charge fault—proceed to Check power.
  • Bad: Charging (green)—backup is working; different issue.

Check power

Goal: Confirm the unit is plugged in and the charger has power.

  • Confirm the backup is plugged into a working outlet. The charger light (often green) should be on. When the outlet is dead, check the circuit breaker.
  • Good: Charger light on. Proceed to Check connections.
  • Bad: Charger light off—check outlet and breaker.

Check connections

Goal: Confirm battery terminals are tight and clean.

  • Shut off power and unplug the unit. Open the battery compartment. Check that terminals are tight and free of corrosion. Clean with a wire brush and baking soda if needed.
  • Good: Connections clean and tight. Proceed to Test battery.
  • Bad: Corroded or loose—clean and tighten, then retest.

Test battery

Goal: Confirm whether the battery is dead or failing.

  • Use a multimeter. A 12V battery should read about 12.6V when fully charged. Below 11V often means the battery is dead or failing. Check the battery age—typically 3–5 years.
  • Good: Battery tests bad or is old—replace it.
  • Bad: Battery tests OK—charger or control board may have failed; call a pro.

When to get help

Call a professional if:

  • The charger light is on but the battery still does not charge.
  • The control board has failed.
  • The unit has error codes you cannot resolve.
  • You are not comfortable with electrical work.

Verification

  • Charger light is green and battery indicator shows charging.
  • Battery voltage reads about 12.6V when fully charged.
  • Test cycle runs the pump on battery power.
  • No charge fault or red light.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Check power Confirm unit is plugged in and charger light is on.
  2. Check connections Tighten and clean battery terminals.
  3. Test battery Multimeter test—below 11V often means replace.
  4. Replace battery Match type and voltage; install and test.
  5. Call a pro Charger on but no charge, or control board failed.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Charger light status
  • Battery voltage reading
  • Battery age
  • Replacement battery model and date

Does the backup show a charge fault?

Red light, flashing, or "charge fault" means the battery is not charging.

Check the battery backup unit. Charge fault: battery not charging—check power and connections. Charging (green): backup is working—different issue.

Yes No

You can change your answer later.

Is the unit plugged in and is the charger light on?

The charger needs power to charge the battery.

Confirm the backup is plugged into a working outlet. Check the charger light (often green). On: proceed to connections. Off: check outlet and breaker.

Yes No

You can change your answer later.

Is the circuit breaker on?

A tripped breaker cuts power to the outlet.

Reset the circuit breaker. On: plug in unit and check charger again. Trips again: possible short—call a professional.

Yes No

You can change your answer later.

Are the battery connections tight and clean?

Loose or corroded terminals prevent charging.

Shut off power. Open battery compartment. Check terminals—tight and clean. Clean corrosion with wire brush and baking soda. Good: proceed to test battery. Bad: fix connections and retest.

Yes No

You can change your answer later.

Does the battery test below 11V?

A dead or failed battery will not hold a charge.

Test with a multimeter. 12V battery should read ~12.6V when charged. Below 11V: battery likely dead—replace. Above 11V: battery may be OK—check charger/control board.

Yes No

You can change your answer later.

Replace the battery

Match battery type and voltage (usually 12V AGM). Disconnect power, remove old battery, install new one, restore power. Run test cycle. Charger should turn green.

Done

Backup is charging

The battery backup is working. Test annually and replace the battery every 3–5 years.

Done

Call a professional

Call if: charger light is on but battery still does not charge, control board has failed, or you are not comfortable with electrical work.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

How long do battery backup batteries last?
Typically 3–5 years. Heavy use or deep discharges shorten life. Test annually and replace when the battery no longer holds a charge.
Why would a battery backup not charge?
Power loss, loose or corroded connections, failed battery, or failed charger/control board. Check power and connections first, then test the battery.
Can I replace the battery myself?
Yes, for most units. Match the battery type and voltage (usually 12V for sump backups). Disconnect power before replacing. Some units require a specific battery model.
When should I call a pro?
Call if: the charger light is on but the battery still does not charge, the control board has failed, or you are not comfortable with electrical work. A pro can also test and replace the battery.

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