I am thinking about upgrading my battery to more heavy duty version. My local dealer has avised against this as do Skoda in the handbook.

When I ran VW's I didn't have a problem and so I don't see problem now as long as it will fit in battery holder. Anyone done this?

Not sure why you'd need to unless running serious amounts of ICE/electronic equipment, but this member was going to fit a second battery in the boot:

http://briskoda.net/forums/topic/178795-its-here/page__st__40

You could PM him re.

What do you need to uprate the battery for?

as VRS said, unless your adding some hefty equipment its not really needed

Batteries have 2 main 'performance' ratings - the ah rating (how much current it can supply over an hour) and the CA and CCA rating (pretty much out dated now, but its how much current the battery is able to supply for 30 seconds until battery voltage drops to around 7v)

If your adding a lot of equipment that will be used with the engine off you want to increase the AH rating of your battery if you want to provide lots of instantaneous current you need a battery with a low internal resistance - the 2 batteries I have added have lots of both (100ah and silly low internal resistance to allow fast recharge and discharge times)