dg wrote:

I am aware that battery life wil be limited, but in considering some
18v models is there any reason why a cheap one from say B&Q will have
significantly less run time than a Dewalt or Bosch Pro model?


Crap bats & chargers...

For cordless stuff the quality of the battery is important even at the
same ampere-hour rating, as this rating might not last for ever...

I had an B&Q PPro drill driver, the bats lasted about 4 months before
they were semi-hopless (would not even hold charge overnight). My
friends dewalt (albeit over twice the cost) faired much better over a
year or two under pro usage conditions.

I suspect the quality of the charger (overcharge protection,
conditioning etc) has a big effect here too.

HTH,

Alex.