Notebook batteries are designed specifically for the specific notebooks brand as well as model. Today notebooks are almost all powered by lithium ion batteries. Lithium ion batteries are lighter, have a better power-to-weight ratio, hold a charge longer (even when not in use for long periods of time), have a longer usable life, and do not have the memory effect to fail prematurely that the previous generation batteries all suffered from.

Lithium ion batteries are also fairly inexpensive to make as compared to the earlier generation of nickel metal hydride batteries. The main shortcoming to lithium ion batteries is as they contain lithium salt dissolved in a highly flammable solvent, which increases the chance of over heating which could result in short-circuits or even flame ups (but these are both extremely rare).

It is a inherited fact that all notebook batteries have a limited time of power supply. A good idea is to check the battery power before buying a notebook.
 
Here is one instant tip to optimize the batteries life is to change the settings in accordance with the energy saving mode of your notebook. These settings will put the hard disk into sleep mode whenever the workload alllows and it will reduce the notebook microprocessor performance in order to maximize its battery life on non intense operations.
In Windows XP, to change your settings for maximum battery performance, do the following... From the system preferences mode of your notebook, select view menu, then choose energy saver option from the view menu. Right click on show details option and choose battery power from the pop-up menu. Finally choose longest battery life from the energy settings menu and click apply and save.

Tips to optimise your notebook batteries are outlined in the following:

It is better to keep your notebook on standby mode when not in use for extended periods of time. Standby mode ensures all current info is saved in RAM with minimum consumption of battery power to maintain it.

It is a good investment to add more memory to your notebook as it saves battery power by reducing Windows dependence on the virtual memory swap file on your hard disk which is a real battery killer. RAM memory spares your battery and can drastically increase your usable battery life per charge.

Try to set the screen brightness of the LCD panel of your notebook to the lowest comfortable level as very bright screen will consume more power from your battery and kill your battery up to 20% quicker then a lower brightness setting.

Charge your notebook battery frequently with your AC adapter. It is very important to clean your batteries metal contacts every couple of months to make it dust and oil free. You can use a cloth moistened with rubbing alcohol to clean your notebook batteries connectors.

Turn of the unused features and technologies of your notebook which are not frequently usable. For example, it is better to eject the DVDs when you are not using them as the optical drive has the tendency of reading them if left in the drive. Also, power down wireless network cards and bluetooth access, both of which rob battery life and may not be in use.

Similarly it is better to disconnect other peripherals such as printers or digital cameras as they can still draw power from your notebook battery even when they are not used.

Turning off or at least disabling the PC Cards, FireWire devices and USB ports when not in use also saves battery power. In fact, disabling internal modems, network cards and USB ports consumes less battery power even when they are on. These devices are easily disabled in Widnows device manager.

Virus scans should be set to run only during the time you are plugged in as full-disk virus scans of your hard drive consumes additional power from battery.

You can use power saver options from your operating system to adjust the CPU processing power. Optimum CPU processes consume additional battery power and hence should be avoided if not running data intense applications. Stop the auto start applications on your notebook, so that your notebook`s CPU can be stopped from doing unnecessary work and loading programs you may not need to use at start up.

With the above mentioned handy tips, you can increase the battery performance of your notebook by up to 35% or more.