After charging it twice my battery eventually went completely flat!!

i recently bought the spare battery and charger with stand from mobile fun. i previously bought one from handtec, it didnt work, the orange light just flashed and the spare battery nor the one that came with my phone would charge. so i sent it back (at my own expense) and ordered the same from mobile fun, who i had bought things from in the past. the first thing i noticed was that the mains charger would not work with the spare battery charger, it had to be plugged into my laptop to work. a pain, but i thought yeah, i can work with that i suppose for the sake of having a spare battery. the next thing i noticed was that after charging, both the spare battery and my original battery only held ten hours, whereas previously with the original battery i' got 20 hours or so. another thing i noticed was that the charger had to 'rest' between charges - if one battery had finished charging and then i put the second in, it would flash orange unless it had had a few hours break in between. then, sometimes i'd leave a battery in charging and annoyingly, several hours later i'd go back and the orange light was flashing and the battery had not charged. this happened several times so i got annoyed and returned it to mobile fun. However, when i went back to charging my battery the traditional way, it only charged to 35% and then discharged very rapidly. just over 24 hour on and i can just about switch it on to see if i have any messages, providing it has been plugged in for a few hours, and leave it plugged in while i check. five/ten minutes later and it has discharged again and that's it for another few hours. as you can imagine i am furious that the extra charger seems to have ruined my very lovely phone. this is as yet unresolved despite contacting the seller and samsung themselves. neither have replied. a very expensive charge has rendered my very expensive phone useless.