I've come across a number of queries referring to this, so I thought I would put it on its own header. Batteries come in standard sizes. Not all manufactures make all sizes. All foreign manuf' but Japanese is probably best. This gives many options for choosing a replacement for a Chinese battery.
If you buy a "build it yourself" machine, and the battery comes with the sulphuric acid in bottles, to put in the battery when you need it, It really could do with a charge to bring it up to normal. At the very least, I recommend standing overnight before use.
These batteries should only be charged at about 0.4 Amp. You can get away with charging at about 2 Amps for a short time on a battery that is a little low. NOT ON A FLAT BATTERY! For these reasons, a car battery charger may damage your battery.
These batteries do not store well. Freshen charge them about once every six weeks if not being used.
How do I know? I worked for a battery manufacturer who was middle man for these batteries, and I prepared them for Lotus who use them as an emergency battery. (The bonnet is opened electrically, so if you get a flat battery, you can't open the bonnet to charge it....hence emergency battery in boot)
Sorry mate, but you have almost certainly killed it! Batteries that get flattened, and are then left discharged are usually junk. If dealt with quickly you may get away with it. Some respond to being left for hours on a very low current. If this doesn't work, then a SHORT burst of high current (30 Min's) might get it going. Batteries discharged below 7.2 volts (on load) are not happy ever again. If it is less than 7.2 V off load.......it's almost certainly a bin job, because if you manage to charge it, it will now be a crap battery.
Have just had a look at the link you provided. Everybody else....... This is spot on for charging and looking after your batteries! At about £35 (+p&p?) it may be a bit stiff for some youngsters though. Put on your Christmas present list! Don't forget! it will work on all later vehicles too, when you move up.