Charger shows E05 undervoltage; charging is slow, intermittent, or will not start.

Safety first: Turn off power at the breaker before opening the charger. Only qualified persons should work inside the panel.

• Check for other heavy loads: Temporarily turn off large appliances (HVAC, ovens, dryers) on the same service and see if the E05 condition improves. If so, the service may be overloaded.
• Inspect input terminals: With power OFF, open the JuiceBox and verify all input terminal screws are tight and conductors are fully inserted. Look for discoloration or heat damage.
• Measure voltage under load: Have a qualified person measure voltage at the JuiceBox while attempting to charge. If voltage sags significantly below nominal (e.g., under 208–220 V on a 240 V system), the branch circuit wiring may be undersized or too long. Upgrading the circuit may be required.
• Try a lower current setting: In the app, reduce the maximum current (e.g., from 40 A to 24 A) and test. If charging becomes stable, this confirms a supply limitation rather than a charger defect.
• Persistent E05 with good voltage: If measured voltage is stable and within spec, but the charger still reports undervoltage, the main control board sensing circuit may be defective and require replacement.