I recommend that, if you have a £400 smartphone that dumps charge and you have to wait a long time for it to charge sufficiently from drained, then take it back & have them replace it. It ain't good enough. Which is a shame because the 800 is a lovely phone, Mango is an excellent OS & the build qual is nice.
I think that there may be more than one flaw with early 800s and I would suggest that if you're having problems, irritating battery behaviour etc, then take it back and ask for an exchange. They should do what T-Mobile did for me - send it for repair (more likely replacement) under warranty.