The processess of facebook, autosync, skype(Imo.im which im using instead of skype) are HUGE battery drainers.
The phone can be actually used for 4-5 days if you don't use 3g network or any other online feautures like skye, facebook chat or autosync.
This battery that i bought is keeping phone's life +20% more than the factory battery.
Also, please keep in mind that this phone is a mid-class, which can't compare with HTC desire phones or similar. Despite of that the phone is doing very well with its characteristics and it's a real traesure for people like me (who don't like touch keyboards).
(I know that in countries like UK and US has their cell phones for free with only just a customer plan, but in countries like Bulgaria this phone worths 370 dollars and again this is mid class for our standarts)