So you bought a new laptop battery and then find that it doesn't last anywhere near as long as the book says that it should.
Of course it could be fitted with low quality cells but there is another reason which causes this, especially if the reason why you bought a new battery in the first place is that your old battery seems like it has worn out. Try this before "negging" the supplier.
All laptops are a careful balance between size and keeping cool. Therefore the cooling system will be compact too and therefor can easily ecome clogged with fluff.
Look at the manual or book and see if you can clean out the fan yourself. On many machines you can and you will be astounded what a difference it makes to the battery consumption, as well as the noise that the fan generates!
We have now had this on several machines and a simple blow out can make a huge difference to the power consumption and therefore the battery life.
If you can get at the fan then a) be very careful not to damage and "off centre" the blades and b) scrape all the ingrained dust off. Also do look in every nook and cranny and wipe with a small paintbrush. Be careful to cover the metal surround with some non-conducting stuff - such as sellotape - as if you short anything out you can find yourself in real trouble! Be careful but do a good job, blowing air from the other direction to which it normally flows.
Try it, and if this helps please do come back and rate this suggestion.