We are on site in our newly purchased Triton 2009 and we have an electric hook up. The battery is getting very hot is this normal ?

Unplug the EHU immediately and work out if you can switch off the battery charger and then plug in the EHU again. That way you won't be charging he battery but will have mains power. It could be a battery problem or a charger problem.

As steamdriverandy has said unplug straight away as long as you can bypass the battery and get mains electric that is the main thing. Try not to let it ruin your holiday easy for me to say! leave it off and get it checked out soon as you can. Check the sides of the battery for swelling/bulging as well. It could be as said battery charger fault or damaged battery. Buy a cheapo multimeter very handy bit of kit and you can then check battery under routine checks in two minutes.
Morphy