I found a great forum post about this on TheBeijinger forum, so I'll repost it here:
A couple of my friends asked my to write a guide for buying Electric Bikes in Beijing. I've copied and pasted my article here because I thought it might be useful to other people.
You can find the original post at http://www.adinobro.com/buying-electronic-bike-beijing.html
So your interested in Buying an electric bike / scooter and while you've seen
them at the stores the manuals are all in Chinese and you've been around China
long enough to know that you can't trust a word that the salesman says. Well
you've come to the right place. I decided I wanted to buy an electric scooter
after I rented one during our holiday in Yangshuo, so when I came back to
Beijing I went online to find out what the deal was. Unfortunately most of the
information I found was really old and out of date. Normally that wouldn't be an
issue but originally the government was planning on banning electric bikes
inside the 4th ring road by 2005. That all changed when carbon pollution became
a hot political issue and now China is actively encouraging electric bikes. Up
until the beginning of the year there wasn't any information about electric
scooters because they weren't bikes because they didn't have peddles and they
weren't motor bikes either. That got cleared up in January when they were
officially classified as bikes because they have zero emissions.
After talking to a number of people the current situation seems to be that
electric scooter and electric bikes are treated exactly the same as bikes except
for the fact that you have to register them. Registration costs about 10 RMB and
if you buy it from one of the smaller shops they'll even do it for you if you're
willing to wait or come back the next day. If you want to get the plates
yourself then you'll need a letter from the store to prove that you bought it as
well as a residency permit and your passport. Unfortunately most of the bike
stores don't sell helmets so you'll probably have to go to Decathlon to buy one.
You'll also want to buy a lock so you can lock your new expensive bike to a pole
Now if all of this sounds like a lot of work there are a lot of reasons why
you might want to buy an electric bike:
1. No more taxi fares.
2. No more waiting on the sidewalk for a taxi.
3. No more sitting in peak hour traffic.
4. It's much more convenient than a car.
5. You have a lot more freedom to explore.
6. It's 100% legal unlike a motor bike.
7. They are really cheap and pay for themselves.
You are interested? Well now comes the hard part. Do you want an electric
scooter or an electric bike?
Feature Bike Scooter
Cost 1,500 to 2,500 (RMB) 2,500 to 4,000 (RMB)
Battery Weight ~15 kg ~25kg
Batter Style Easy to Carry Needs a trolley