hi, yes there is but you will need a volt meter.
1. with EHU disconnected take a reading from the battery at the terminals, should read about 12v ish if the battery is not flat.
2. with EHU connected take another reading if the charger is working it should now read 13.8v. if it is still around 12v the charger is not working.
3. also check the main power lead, on the EHU cable van end to make sure there is power to the charger. ie, try the 240v mains lights ect.
also look at the plug behind the charger to make sure it is connected (looks like a kettle plug) sometimes these can work loose while towing over time they the disconnect themselves "happened to me once"
if all else fails, and you happen to be away, get hold of a cheap charger plug it into one of the 240v sockets and charge the battery that way untill you get home.
hope this helps.