Hi All,
My rear screen heater packed up, now the front has done same.
Switches illuminate but no demist on either.???
It's a 2009 RR Sport 2.7 V6 Auto HSE.
What can I do about it?

It's very possible your main battery is in a low state of charge and the power management module has turned off the screen heaters to preserve power.

Try charging up the battery fully overnight with a smart charger.

If that doesn't resolve the issues have someone check out your battery and alternator health. 2008 MY Java Black TDV8 HSE

Thanks Paddy, I wouldn't have thought of that.

Any special issues I should look out for when disconnecting/charging/reconnecting?

Talk to any one who has worked with vehicles for a long time and they'll tell you horror stories about batteries exploding causing loss of eyes/burns. Wear eye protection at least.

Many of us regularly connect smart chargers to the battery without disconnecting the battery from the vehicle with no ill effects.

If using an old-fashioned unregulated charger it is safer to disconnect the battery first.

Before disconnecting battery unlock car and open bonnet and then let car go to sleep - takes about 10 minutes or so then disconnect battery; earth lead first.

Connect charger to battery - then switch on charger.

When charged - disconnect charger from mains first then disconnect from battery. Allow surface charge to dissipate for an hour or two.

Reconnect battery positive lead first then earth. 2008 MY Java Black TDV8 HSE