iPhone battery is not lasting long.

How long is "not that long"? Is it around what the manual says to expect?

Options:

1. Charge it more often and until it's done.
2. (1b) Carry a portable charger.
3. Use it less.
4. Turn some features off (i.e. data connection) or down (i.e. brightness). This option will have limited success, if any.

iPhone and iPod Touches don't really have the greatest battery lives to start with. If it's unusually short (a few hours or less) then try going to your local Apple store and get the battery replaced. If it's a new device then it should still be under warranty.

If you have a warranty call support and try to get it replaced. Other wise try to carry a external battery source or some way of keeping it charged

The 3GS has an estimated 10 hours, Apple is normally conservative with battery life estimates. If it does not feel like it's lasting anywhere near 10 hours, then I'd assume something is defective. I would go to Apple to check it out. To increase battery life, turn down brightness, turn off wifi / 3G when you can, turn off push notifications, go to the appstore and get a 3rd party browser then restart your device and do not open Safari ( once open, it stays open eating at memory and CPU resources which can lower battery life ).

If you're iPhone is still under warranty, then take it. Otherwise, you may need to replace the battery (See below)

https://www.iphonebatteryrepair.com/

very ture but yet on a personal level it is not so good so why is it that to os on the iphone sucks.

The question is, what have you been using it for? The battery life is certainly going to be reduced under heavy use, resource intensive applications such as games, or active use of networking components.