boot up your operating system, see the little battery bar down there? Then right click, change the setting portable/laptop to max battery and you will get it but it is kind of annoying because the screen turns off every 1 minute if you don't touch it but you will have about 30-40 more minutes of battery life!
I recently purchased a Acer Aspire 3002LCi, and it says the battery life can be up to 1.5 hours depending on usage and configuration. How can I get all 90 minutes, at the moment it goes for a little over an hour. Also is it possible to get a stronger battery for it?