Just resurrecting this rather old thread, my iPhone battery drain problems are now all solved.
One was solved by fitting (eventually) a decent battery.
One was solved under warranty (bought used from a reasonably reputable supplier/repairer) and I actually have no idea how, but I have my suspicions (see below and think it through....).
The third was effectively "given up on" by the (fairly local to me but with a national presence) firm working on it and they refunded me what I'd paid to initially fit a new battery, after which it had got much worse and stayed that way after multiple further tests and battery swaps. I wasn't happy, especially when I happened (soon after) to see a random "watchdog-type" consumer program on the BBC which rather "named and shamed" this particular company for failing a significant number of customers!
So I spoke to the company that fixed #2 and sent #3 to them, paying £15 for a diagnostics service. As #2 and#3 had been giving almost identical symptoms I reckoned it was worth trying.
They diagnosed a faulty charger chip, costing £60 to replace less the diagnostic charge which would be deducted if I went ahead.
I did and all is well, battery life is the longest I've ever seen on an iPhone.
Since I got it back I've only charged it twice, once on receipt and once just over 2 days ago.
Currently it's showing 49 hours of use (including standby) and 61% battery remaining. It could last for over 5 days!
Not sure what lessons I've learned, but I have identified one iPhone repairer that do seem to know what they are doing, and one that doesn't.....