Charging system when driving

We Have the Sargent 500 PSU fitted to our 2013 Broadway when driving it does not seem to put much charge into the batteries according to the display. Recently we did a 600 mile journey over 2 days in Spain and the display read 65% before the journey, and after it only read 85%. Yesterday before we came home from Southport the display read 87% after 1-1/2 hour journey home it read 91%, surely the display should read near to 100% on these journeys.
When our Broadway went back to Auto Sleeper last month for repairs I told them how the system was working and they said they thought it was a faulty unit but they had reset it, and if we had further problems let them know, anyway I rang them and they said check all fuses, all ok. I've been on to Sargent technical this morning and they say it's working ok as the display is only an estimate, but when I get home and go on hook up after a period of time the display goes slowly up to 100%.   

Anyone else noticed how theirs is working.

John.

Does the Broadway have an absorption type fridge? Is it on while you are travelling?

If so, it will be taking maybe 6 Amps from the alternator all the time that it is able to provide that much power (and it may not be able to all of the time, depending on other vehicle electrical loads). This (if true) would significantly reduce the remaining power available to charge the leisure battery via the split charge system.

Yes mojo it has a absorption fridge and I have it on when travelling so next time out I'll have the fridge switched off and see how it goes.

Thanks,
John.

Thanks again Peter.