You had ask about a battery to buy so I thought I'd let you know what I had bought. If someone else wants this information, only provide it without my forum name included and remember that it's at your own risk when buying from aliexpress.com.
I saw your post about wanting to find an extra battery to buy. I can tell you about a company that I and another guy has bought a 48V 14ah battery that came with a 2A charger. I haven't used my battery all that much as I've only rode my bike for 4 miles using it and it hasn't given any problems. The other guy has used his for 100 miles so take this information for what it's worth.