12v adaptor off the main battery

[TravellingChick]

I have a set of these:

http://www.pfjonescamping.co.uk/caravan ... rrency=gbp" onclick="window.open(this.href);return false;

Which I bought last year and have worked fine until recently. The satnav doesn't appear to be getting enough power to stay on for more than 2 mins and the phone takes forever to charge up too.

The lighter socket piece is getting seriously hot and smelly so clearly not working properly.

I expected them to last longer than a few months with sporadic use at that tbh. Anyone else had the same problem? Would it be better to run it off the leisure batter when I'm driving?

They're only a few quid but I'd rather not have to buy 2 sets per year - anyone using anything more reliable?

TIA
Sarah