Generally speaking, the hard drive should be fairly easy to upgrade. Most notebooks use a standard 2.5" drive that you can find @ online shops or in a few brick & mortar computer stores.
As for other parts....it really depends.
For example, extra/replacement batteries are usually model/unit specific. So if you were looking to buy the Battalion 101 E-Turbo (actually the Aopen 1557GLs), you could buy replacement batteries from other vendors who sell this unit too. The same would go for a replacement power adapter.
Was there some specific part you had in mind?
Hope this helps.