Why have you posted the same question in two threads?
Never heard of the site until now, but having searched on google I've found these two links:
http://www.psp-hacks.com/forums/f126/scam-psp-sites-t235491/
http://flippa.com/auctions/62856
Seems that they're a drop shipping company (according to the second link), meaning that whether you can trust them will depend on the reliability of the suppliers that psppandora.co.uk are ordering from (unless of course they just steal your money). There are sites out there that sell batteries for as low as £4 (e.g. dealextreme/focalprice), so considering that this (probably) isn't being shipped from the UK your dad's been ripped off.
One person in the first link said that they got their item after 10 days, so I wouldn't be too worried for now, but as I said there isn't a lot of info to go off on.