Elddis 12v power issue

[Fahrenheit]

Hi all hope someone here can help or had the same issue.
Just returned from 5 days away but on day4 we lost all 12 power, have checked the battery and charger is putting ot 13.8v. Checked by on site engineer. Im guessing there is a control board or voltage regulator somewhere that may have gone but just dont know. When i turn van electric on i only get 9.5 volts on readout and as soon as i try any load or switch lighting circuits on. The power just dies. Van is an elddis jetstream 98. help!!!!!!!!!!

 

[Damian]

Although the charger may be putting out 13.8v, what is the battery voltage at the battery terminals with mains power switched off?
Don't rely on an on board voltmeter, they are notoriously inaccurate.