Question 1

Battery cannot be charged, LED blinks indicating reversed polarity

Accepted Answer

Possible cause: Reversed polarity connection. Check and correct cables and connections

Question 2

Battery cannot be charged, LED is continuously lit indicating battery connection lost during charging

Accepted Answer

Possible cause: Battery is no longer connected or fuse in connection cable has failed. Check cables and connections, inspect and replace automotive fuse in the connection cable

Question 3

Red flashing LED: A line is disconnected

Accepted Answer

Possible cause: Broken or loose cable connection. Check the cables and connections.

Question 4

Red flashing LED: Defective battery

Accepted Answer

Possible cause: Battery has failed or internal cell issue. Replace the battery.

Question 5

Red permanently lit LED: No supply voltage

Accepted Answer

Possible cause: Mains power interruption or blown internal fuse. Check the cables and connections to the mains supply. Check if the fuse has triggered and replace if necessary (type F 16 A / 5 x 30 mm).

Question 6

Red permanently lit LED: Inverse polarity

Accepted Answer

Possible cause: Battery terminals connected incorrectly (+ to -). Connect the IU0U automatic charger with the correct polarity. Check and replace the fuse if blown.

Question 7

Red permanently lit LED: Thermal overload

Accepted Answer

Possible cause: Excessive ambient temperature or blocked ventilation. Improve the ventilation of the charger, make sure no ventilation openings are covered, and reduce ambient temperature.

Question 8

Status LED slowly flashing Red (Undervoltage or overload)

Accepted Answer

Possible cause: Battery undervoltage, battery overload, or defective battery. Check the battery. Switch the battery charger off and on again. Replace the battery if defective.

Question 9

Status LED slowly flashing Red (Overheating)

Accepted Answer

Possible cause: Poor ventilation or excessive ambient temperature. Improve ventilation around the charger and battery. Ensure vents are clear and reduce ambient temperature.

Question 10

Status LED permanently lit Red

Accepted Answer

Possible cause: Short circuit or reversed polarity. Connect the charger with correct polarity. Rectify the short circuit. Check and replace triggered fuses if necessary.

Question 11

Status LED double flash Red

Accepted Answer

Possible cause: Fan fault. Check the cooling fan for accumulated dirt, blockage, or physical damage.

Question 12

Status LED slow double flash Red

Accepted Answer

Possible cause: Starter battery connection fault. Check the starter battery connection (ESB) for short circuits.

Question 13

Voltage in the battery does not rise after connection and commissioning

Accepted Answer

Possible cause: Poor contact between terminals and battery poles or discharged/defective battery. Check voltage increase on display during charging, ensure proper contact, and clean battery poles.

Question 14

Battery is not fully charged after approximately 20 hours

Accepted Answer

Possible cause: Defective battery unable to accept charge (terminal voltage <= 10 V for 12V battery or <= 20 V for 24V battery). Disconnect charger, wait a few minutes, measure terminal voltage with a multimeter. If <= 10V (12V batt) or <= 20V (24V batt), replace or professionally test and dispose of the battery.

Question 15

Battery discharges quickly without load

Accepted Answer

Possible cause: Battery is too weak to hold a charge (terminal voltage < 12 V or < 24 V). Measure terminal voltage with a multimeter. If under 12V / 24V, have the battery tested by a specialist or dispose of it properly.

Question 16

Red 'Reverse Polarity' LED lights up

Accepted Answer

Possible cause: Battery terminals are connected with reversed polarity (+ to -). Switch off the battery charger and swap the terminal connections.

Question 17

Red 'Error' LED lights up after switching on

Accepted Answer

Possible cause: Battery terminals connected with reverse polarity. Switch off the battery charger and correct the connections (red to positive +, black to negative -).

Question 18

After connecting and starting, the voltage in the battery does not increase

Accepted Answer

Possible cause: Poor contact between terminals and battery poles, or faulty connection. Measure with a multimeter to verify voltage rise at terminals during charging, check terminal contact, and clean battery poles.

Question 19

Battery discharges itself shortly after charging without load

Accepted Answer

Possible cause: Battery is too weak to hold a charge (terminal voltage < 12 V). Measure terminal voltage with a multimeter. If < 12 V, have the battery checked by a specialist or dispose of it.

Question 20

Battery is not fully charged after approx. 20 hours

Accepted Answer

Possible cause: Battery is defective or deeply discharged (cell damage/sulphation). Disconnect charger, remove clamps, wait a few minutes, and measure terminal voltage. If 12V battery reads 10V or lower (or 20V or lower for 24V battery), the battery is defective. Have it tested by a specialist or replace it.

Question 21

Battery discharges quickly even without load

Accepted Answer

Possible cause: Battery is too weak to hold a charge. Measure voltage with a multimeter. If below 12V for a 12V battery (or below 24V for a 24V battery), the battery is exhausted/weak. Replace or have it checked by a professional.

Question 22

Red status LED slowly flashing

Accepted Answer

Possible cause: Battery undervoltage or battery overload. Check the battery, switch the battery charger off and on again, or replace a defective battery.

Question 23

Red status LED quickly flashing

Accepted Answer

Possible cause: Battery or battery charger is overheating. Improve the ventilation of the battery charger or battery, ensure ventilation openings are not covered, and reduce ambient temperature if necessary.

Question 24

Red status LED permanently lit

Accepted Answer

Possible cause: Short circuit, reversed polarity, or broken internal fuse. Connect the battery charger with correct polarity, remove the short circuit, and contact customer service for internal fuse replacement.

Question 25

Red 'Error' LED lights up

Accepted Answer

Possible cause: Battery terminals connected with reverse polarity. Switch off the battery charger and correct the connections.

Question 26

Charger does not switch on and blue charging display remains off

Accepted Answer

Possible cause: Battery is already fully charged (> 13.2 V) or deeply discharged. Switch off the charger and disconnect the terminals. The charger has a safety control function preventing charging under these voltage conditions.

Question 27

Voltage in the battery does not increase after connection and start

Accepted Answer

Possible cause: Poor contact between terminals and battery poles. Clean the battery poles and verify proper terminal contact using a multimeter.

Error Code / Indicator	Symptom / Meaning	Step-by-Step DIY Fix	Suggested Actions
`N/A`	Battery cannot be charged, LED blinks indicating reversed polarity Possible Cause: Reversed polarity connection	Check and correct cables and connections	DIY Safe
`N/A`	Battery cannot be charged, LED is continuously lit indicating battery connection lost during charging Possible Cause: Battery is no longer connected or fuse in connection cable has failed	Check cables and connections, inspect and replace automotive fuse in the connection cable	DIY Safe
`N/A`	Red flashing LED: A line is disconnected Possible Cause: Broken or loose cable connection	Check the cables and connections.	DIY Safe
`N/A`	Red flashing LED: Defective battery Possible Cause: Battery has failed or internal cell issue	Replace the battery.	DIY Safe
`N/A`	Red permanently lit LED: No supply voltage Possible Cause: Mains power interruption or blown internal fuse	Check the cables and connections to the mains supply. Check if the fuse has triggered and replace if necessary (type F 16 A / 5 x 30 mm).	DIY Safe
`N/A`	Red permanently lit LED: Inverse polarity Possible Cause: Battery terminals connected incorrectly (+ to -)	Connect the IU0U automatic charger with the correct polarity. Check and replace the fuse if blown.	DIY Safe
`N/A`	Red permanently lit LED: Thermal overload Possible Cause: Excessive ambient temperature or blocked ventilation	Improve the ventilation of the charger, make sure no ventilation openings are covered, and reduce ambient temperature.	DIY Safe
`N/A`	Status LED slowly flashing Red (Undervoltage or overload) Possible Cause: Battery undervoltage, battery overload, or defective battery	Check the battery. Switch the battery charger off and on again. Replace the battery if defective.	DIY Safe
`N/A`	Status LED slowly flashing Red (Overheating) Possible Cause: Poor ventilation or excessive ambient temperature	Improve ventilation around the charger and battery. Ensure vents are clear and reduce ambient temperature.	DIY Safe
`N/A`	Status LED permanently lit Red Possible Cause: Short circuit or reversed polarity	Connect the charger with correct polarity. Rectify the short circuit. Check and replace triggered fuses if necessary.	DIY Safe
`N/A`	Status LED double flash Red Possible Cause: Fan fault	Check the cooling fan for accumulated dirt, blockage, or physical damage.	DIY Safe
`N/A`	Status LED slow double flash Red Possible Cause: Starter battery connection fault	Check the starter battery connection (ESB) for short circuits.	DIY Safe
`N/A`	Voltage in the battery does not rise after connection and commissioning Possible Cause: Poor contact between terminals and battery poles or discharged/defective battery	Check voltage increase on display during charging, ensure proper contact, and clean battery poles.	DIY Safe
`N/A`	Battery is not fully charged after approximately 20 hours Possible Cause: Defective battery unable to accept charge (terminal voltage <= 10 V for 12V battery or <= 20 V for 24V battery)	Disconnect charger, wait a few minutes, measure terminal voltage with a multimeter. If <= 10V (12V batt) or <= 20V (24V batt), replace or professionally test and dispose of the battery.	DIY Check / Tech Fallback
`N/A`	Battery discharges quickly without load Possible Cause: Battery is too weak to hold a charge (terminal voltage < 12 V or < 24 V)	Measure terminal voltage with a multimeter. If under 12V / 24V, have the battery tested by a specialist or dispose of it properly.	DIY Check / Tech Fallback
`N/A`	Red 'Reverse Polarity' LED lights up Possible Cause: Battery terminals are connected with reversed polarity (+ to -)	Switch off the battery charger and swap the terminal connections.	DIY Safe
`N/A`	Red 'Error' LED lights up after switching on Possible Cause: Battery terminals connected with reverse polarity	Switch off the battery charger and correct the connections (red to positive +, black to negative -).	DIY Safe
`N/A`	After connecting and starting, the voltage in the battery does not increase Possible Cause: Poor contact between terminals and battery poles, or faulty connection	Measure with a multimeter to verify voltage rise at terminals during charging, check terminal contact, and clean battery poles.	DIY Check / Tech Fallback
`N/A`	Battery discharges itself shortly after charging without load Possible Cause: Battery is too weak to hold a charge (terminal voltage < 12 V)	Measure terminal voltage with a multimeter. If < 12 V, have the battery checked by a specialist or dispose of it.	DIY Check / Tech Fallback
`N/A`	Battery is not fully charged after approx. 20 hours Possible Cause: Battery is defective or deeply discharged (cell damage/sulphation)	Disconnect charger, remove clamps, wait a few minutes, and measure terminal voltage. If 12V battery reads 10V or lower (or 20V or lower for 24V battery), the battery is defective. Have it tested by a specialist or replace it.	DIY Check / Tech Fallback
`N/A`	Battery discharges quickly even without load Possible Cause: Battery is too weak to hold a charge	Measure voltage with a multimeter. If below 12V for a 12V battery (or below 24V for a 24V battery), the battery is exhausted/weak. Replace or have it checked by a professional.	DIY Check / Tech Fallback
`N/A`	Red status LED slowly flashing Possible Cause: Battery undervoltage or battery overload	Check the battery, switch the battery charger off and on again, or replace a defective battery.	DIY Safe
`N/A`	Red status LED quickly flashing Possible Cause: Battery or battery charger is overheating	Improve the ventilation of the battery charger or battery, ensure ventilation openings are not covered, and reduce ambient temperature if necessary.	DIY Safe
`N/A`	Red status LED permanently lit Possible Cause: Short circuit, reversed polarity, or broken internal fuse	Connect the battery charger with correct polarity, remove the short circuit, and contact customer service for internal fuse replacement.	DIY Check / Tech Fallback
`N/A`	Red 'Error' LED lights up Possible Cause: Battery terminals connected with reverse polarity	Switch off the battery charger and correct the connections.	DIY Safe
`N/A`	Charger does not switch on and blue charging display remains off Possible Cause: Battery is already fully charged (> 13.2 V) or deeply discharged	Switch off the charger and disconnect the terminals. The charger has a safety control function preventing charging under these voltage conditions.	DIY Safe
`N/A`	Voltage in the battery does not increase after connection and start Possible Cause: Poor contact between terminals and battery poles	Clean the battery poles and verify proper terminal contact using a multimeter.	DIY Check / Tech Fallback

Dometic PerfectCharge

Technical Specifications

Master Troubleshooting & Diagnostics Matrix