How long should a fully charged iPhone 4 battery last?

Got a used iPhone and just wondering

This isn't a tech answer but mine last all day, with about 20%. I'm on it alot to.

It really depends on how you use it. I use mine basiclly quite a lot. So I can last mine for maybe 4-5 hours. But someone who doesn't use theirs a lot, lets say a person who only texts and uses their phone for like informational stuff to look on Internet can make it last all day. It all depends on usage. You can even change the brightness of your screen dimmer to make it last longer

It all depends what you use it for, a new iphone should be up to 8 hours of talk time on 3G, 8 hours of Internet use on 3G, 10 hours of Internet use on Wi-Fi, 10 hours of video playback, or 40 hours of audio playback on a full charge at original capacity.

Since yours is used you can either change the battery or have it checked out.

If you dont use it often, or dont play games constantly (games that use intense graphics like NOVA) ten it should last several hours, even more. I have lasted quite some time on 50% battery alone and on occasion I dont charge my phone for several days. Dont worry, the battery WILL last.