you need something like thish ttp://cgi.ebay.co.uk/NEW-MAINS-230V-TO-12V-POWER-ADAPTER-CONVERTER-AC-DC_W0QQitemZ110320766879QQcmdZViewItemQQptZUK_ConsumerElectronics_PowerAdaptors_SM?hash=item110320766879&_trksid=p3286.c0.m14&_trkparms=72%3A1301%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318ditch the ciggie lighter end and just connect it to the devicethough you will have to check the power your " i cannot say the word " system needsas you might need something with a little more ooompppph ( they have them on ebay )
Why don`t you just wire up a solinoid valve like you would in a van to the static battery.
dave, that ebay item i listed will be ok thenits just a plug in the wall that produces 12 V powerjob doneoh and NWH, sorry to destroy the illusion, i dont have a shed im afraid im too poor for a shed