If your laptop has a removable bell battery, when the longevity of the charge starts to suffer, you can go on Amazon and find a replacement battery for the model of laptop that you have. All of a sudden you may double or triple the amount of time you can run on battery only.
A great way to make your new battery last is not use it. When your laptop has a battery in it, the heat from the laptop as well as constantly charging it can degrade the quality of the battery over time. So when you have a nice fresh battery, throw it in your laptop case or your backpack and keep on using your original battery if you're the kind of person who mostly plugging in to an outlet when you sit down on your laptop.
Then when you're in one of those situations where there's no outlet available, throw in your new battery and the lifetime of your battery will be considerably longer than the one you're using everyday. Once you get back to an outlet and charge that battery up, switch out your battery to your everyday battery.
Another thing is these batteries aren't too expensive so if you want you can buy two or three extras and just keep them in your backpack. This is especially good if you're traveling.
Another thing if you have an old hard drive not an SSD, I highly recommend upgrading. The hard drive sucks a tremendous amount of power, when I have graded mine from an HDD to an SSD I literally doubled the battery time on my laptop.