If you are going to buy batteries I would buy from the US
What does which country you buy a battery from make a difference in anything but shipping speed? You do realize that all these batteries are either entirely made in China or the components are and they are assembled in a another country? I am genuinely curious.
DX, in specific, is just a vendor located in the heart of all these factories and they sell overruns at deep discounts. Of course, they now sell a ton of first run and branded stuff and the prices for those are definitely not cheap. All that said DX is hit or miss.
For batteries, there are literally dozens of each type of battery at DX. If you stick to the batteries that get good reviews, you should be fine. It takes them forever to ship out. Its not the shipping that is slow (its normal speed) but it takes them 2 weeks just to package and send the order. So only order from them if you are not in a rush.
I buy from them all the time, but I have developed a love/hate with DX. In general, if you get something that seems too cheap to be true, its real but the product only lasts a few months. As an example of what I am referring to, I have a bin with a half dozen $5 power regulated flashlights (that sell at $40+ at a place like Amazon), they all develop some annoying problem after a couple months that renders them useless. I have 2 flashlights I got for around $30 and they are working well for many months.