Replacement batteries can be difficult to source through the retail channel as there's not a large demand for them. Online is usually best. It's almost impossible to tell whether your're getting a genuine one, but avoiding anything that looks too cheap is usually fairly safe. I'm not familiar with this phone - does it have a user-replaceable battery or is it sealed?
Also, if it's fairly new, you could try asking for a replacement under warranty. If not, the lack of support might be down to age?? If it's not within warranty and it's a sealed device, ti might be cheaper to buy a new phone than to pay for the battery to be replaced.
