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I'm not familiar with the Hymer electrics, and I'm sure that someone that is will be tempted to reply shortly.

It's difficult to diagnose problems at a distance, since wiring and components vary tremendously from 'van to 'van, and things get more difficult if modifications have been made.

First of all - Don't Panic - there is a distinct possibility it will be something simple. A bit of reassurance and a bit of diagnostic work may help.

Whilst Hymer just might differ, on all my 'vans to date you would leave both the 12V master panel switch and the 12V setting on the fridge on whilst travelling, as you seem to be doing. Not turning off at the panel should cause no problems, and on-site you would no doubt turn the fridge to mains or gas anyway.

The fridge is usually wired across the leisure battery(ies) but with a relay switch in the circuit which senses output from the alternator, ensuring that the fridge only draws current whilst the engine is running (and producing a charging current).

Hence, if everything is OK, any current drain from the leisure batteries is compensated by them simultaneously being on charge. Stop the engine, and the relay takes the fridge out of circuit.

Two potential problems here -

1. The charging circuit from the alternator is protected by a fuse in-line to the leisure batteries somewhere. If this has blown, the fridge still goes into circuit when the engine is started and then depletes the leisure batteries (since they are not being charged due to the blown fuse). Been there, done that, completely dead batteries after long drive to Lakes. Remedy, check and replace the fuse.

2. The output from the alternator is insufficient to both drive the fridge and charge (all the) batteries. Can only really be checked by a multimeter, but might show up if switching all vehicle lights on with engine running. Remedy, auto electrician.

It occurs to me that the above could also result from a bad connection in the alternator charging circuit.

On most standard-fit motorhome charging systems, leaving the charger on won't 'fry' the batteries. Ultimately the charger will step back to a 'float' charge. Haven't had my batteries get really hot though.

I should:

1. Check for the blown fuse as above (easy option)

2. Turn everything electrical off (esp. fridge) and run the engine and see if the batteries recharge (if they don't suspect the alternator charging circuit or batteries). If they do, you should re-check at intervals to see if they hold it.

3.Turn engine and everything electrical off except the mains charger and see if the batteries recharge (if not - batteries or mains charger are suspect). If they do, you should re-check at intervals to see if they hold it.

For quickest conclusion, you really need a voltmeter or multimeter to measure the voltage at the battery when either charging method is being used. It should be well above 12.7V (maybe 13.8V to 14.2V) and you should see it go up immediately the battery goes 'on charge. With this you can rapidly diagnose or eliminate any charging circuit issues. If this reading is OK, but battery won't hold charge, you either have a constant drain on the battery from somwhere, or it is dead.

Hope this helps!
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