Well, you could check your powersupply, alot of the time when your battery isn't charging it's the problem of the powersupply. Check your line to see if there is a short in it or try another powersupply. If it's not the line/cord then you should check to make sure your laptop is getting in enough power to power in the first place.
It works like some replacement powersupplies for cameras, they do the job at 'powering' the camera but it won't give you enough juice to power it and then charge the battery, i'd assume it's either the line or the unit itself thats having some connection issues with actually pulling power and retaining it.