Why don't phones have good battery life?

They're getting better. To keep a phone battery living longer, you must let the battery run low, try and run it too its lowest point. I always run my iphone to 7% then charge it up because if you charge it too often when its got enough charge already, it relies more and more on the power cable keeping it charged.

turn your screen brightness half way between dark and the middle. Don't have it on an option like auto adjust because it sucks a bit of the battery just waiting to adjust, helpful tool but can drain it a bit.

(If you have an iphone or android) Delete background running apps like Email apps auto update apps, switch them to manual update it will keep the battery from being used on an app that's not even being used by you.

a few options there to help keep your battery running well because batteries today aren't that bad, they're pretty decent.

not all phones, i have a LG GS101 and the battery lasts about 2 weeks (it has a battery that lasts 800 hours on standby)

it's a basic phone, so thats the reason it has such a long battery life, the more features you start adding and using start to reduce the battery life, GPRS uses the most battery life, activate this and watch your battery drain very quickly.

In my opinion, every phone is different. For example, I have a Droid Razr Maxx and I am very happy with the battery life. Long story short, look at the specs first and then decide what main features you wan your phone to have. The bottom line is - not every phone has a bad battery life. (It also depends how you use your device and what you use it for)

A lot of phones do have good batteries the galaxy note 2 has a battery that's lasts for 9-10 hours and the iPhone lasts 8 hours so they are pretty good and are getting better

Depends on how you use it

Also if it's not a new device, lets say you got it 2 years ago, it's time to replace the battery. I replace the battery in my devices, even iPhones, after 2 years of use. It gives me optimal battery life.

^ I have a MyTouch 4G and the stock battery was crap. I took that out and I put in a Anker 1550 mAh battery and my battery life has been the best!

Phones do have good battery life in comparison to what they are capable of doing. Compared to older phones like @roguekiller23231 mentioned, yea they don't have good battery life. In my opinion I would say the overall quality of today's phone batteries is far from high quality.

I get a good day and a half out of mine... that seems "good" to me.

It's all down to all the fancy graphics, colours, animations - all the "pretty" things that modern smart phones have. All these facilities take resources and sap battery power. I still have an elderly bog-standard Nokia that does nothing fancy at all, complete with its original battery and the capacity on that is STILL ridiculously long. Lasts for days! The same can apply to your home computer if it's perhaps not in the first flush of youth. Knock back a whole lot of graphics, animations and colours, etc. in the properties and there is a quite noticeable speed gain. I don't know if any of this can be applied to a phone.