In article ,
Sam Bond wrote:
What type of power supply are you going to use ?

12v 7ah SLA.

Is that a type of battery? I assume it is by the 'ah' description. A 100%
efficient 200 watt amp running at full power would flatten it in minutes.
And car booster amps are anything but 100% efficient.
For a reasonable portable outdoor system which will run for a couple of
hours reliably, you're looking at a decent sized car battery - say about
45 Ah. You don't want to flatten the battery if it's a lead acid type as
this will shorten its life.

--
*Gravity is a myth, the earth sucks *

Dave Plowman London SW 12
RIP Acorn