Summary
It's pretty easy to lie about what's in a battery because people don't open
them to check inside (and you shouldn't). The label is supposed to tell you
what's inside, but that is not always the case! The good news? You can
digitally verify it.
I have been scammed this way but noticed in time. It's about the capacity, sometimes the label will claim it has more capacity than it really has. If you want to know how to check this, go down to "How to check".
Background
I recently bought a new battery for my laptop via the Internet. I checked the
type (in my case A32-N56), the voltage (10.8V) and the milliampère-hour
(5200mAh). The battery arrived in neat packaging, the label listed a couple
types among which A32-N56 (so it was a replica, but it could still be fine) and
it read 10.8V and 5200mAh. All fine.
First thing I did was check the battery life: charge it to 100% and see how long it takes to discharge during normal use. I remember that the original lasted about 4 hours. This new one didn't even get to 2 hours!
After a few hours of searching I found the problem: they sold me a 4400mAh one! Whether it's the webshop's or the supplier's fault I don't know so I won't name the shop, but it's an intentional scam. An error on the product page could have happened, but the battery's label also (incorrectly) stated 5200mAh.
It is usually not needed to check the original battery, but you should if you ordered a replacement one.
Linux
(If you don't know what 'Linux' is, go down to Windows)
On Linux it's pretty easy. Open a terminal and type:
sudo apt-get install -y acpi
Or something similar for yum or pacman. Once this is done:
acpi -i
This tells you how many mAh your battery was designed for and also its wear
level.
If your battery's label lists Wh (Watt-hour) instead of mAh, you have to multiply the value by the Voltage. So if you got 5200mAh and 10.8V then 5200 × 10.8 = 56160. Divide this by 1000 to get about 56Wh.
Windows
On Windows you have to install an application like NirSoft BatteryInfoView (direct download). After downloading and opening it, you probably get a screen like this:
Double click on the application (blue arrow in the image). It will then ask you to extract, but that is not needed:
Click "Run". You might get more warnings but you can just click 'continue' or 'run' or 'ok' until it eventually starts...
You should see something like this:
The most important field is "Designed Capacity". On some batteries the capacity is written in Wh (Watt-hour), in that case it's easy: just compare the label's value with the designed capacity and make sure it's the same.
Most batteries use mAh though, and in this case there is a small calculation: divide the Designed Capacity by the Voltage. The result will be mAh.
For example in the image it says 56.940mWh and 10.972V, so what you need to do is 56.940 / 10.972 = about 5.190 Ah (or 5190 mAh, like it says on the label).
Mac OS X, Android, etc.
I don't know! If someone knows, send me an
email or
tweet!
In the Netherlands you have a minimum of 7 days, starting at the day of delivery, in which you can return the product (if it still looks/works like new) and get your money back. You may need to pay for shipping, though some companies are kind enough to let you return it for free. Note that I'm only sure about this for "remote sales", like by phone or over the Internet, shops are different.
I was able to use this and the shop was kind enough to pay for the shipping. By now I've gotten the money back.
Internationally, I'm not sure what your rights are. You are expected to know your laws, though, so I'm sure you can ask pretty much anyone ;-)
Replies are welcome! Send me an email or tweet. Additional information will be added to the page, with your name if you want.