how long should i charge my iphone4 for the first time??urgent!!!

Until it reaches the 100% of charge. It has Litium batteries, desn't have the "memory effect". It is recommended once a month to dry the battery until the iPhone gets powered off and recharge it during all night to recalibrate the battery

You can't over charge an iPhone battery. Charging automatically stops when the battery reaches full capacity. LI batteries have no memory effect so you can charge whenever you like. Apple does recommend that you let the phone completely discharge(turn off on its own) and then re-charge to full capacity once a month. Doing so will help maximize the life of your battery. So, when you first get your phone, charge till full then start enjoying your phone.

"i thought it is necessary to drain all the battery to 0% and charge it to 100 % everyday??"

Nope. By the way, my phone's battery was at 75% capacity new out of the box.

i thought it is necessary to drain all the battery to 0% and charge it to 100 % everyday??

No. In fact, you can't drain the battery to 0%.

"so if i forget to unplug the charger even though the battery are charged to full , it does not affect the battery lifespan?"

Nope. It won't "cook" the battery.

so if i forget to unplug the charger even though the battery are charged to full , it does not affect the battery lifespan?

No. Charging stops completely when your battery reaches full capacity.

Read my initial post again:

You can't over charge an iPhone battery. Charging automatically stops when the battery reaches full capacity. LI batteries have no memory effect so you can charge whenever you like. Apple does recommend that you let the phone completely discharge(turn off on its own) and then re-charge to full capacity once a month. Doing so will help maximize the life of your battery. So, when you first get your phone, charge till full then start enjoying your phone.

You can charge your phone whenever you like/need. You can't overcharge it. Charging whenever you like will do no harm. Apple only recommends you fully discharge once a month:

http://www.apple.com/batteries/iphone.html

debbie chew wrote:
sorry . what do you mean by overcharge ?means although it has reached 100 % but i still do not unplug it?
and.. whenever i charge,i have to charge up to 100 % isit?
btw,how to log out my yahoo mail on my iphone?

You can charge the phone at any time, you can unplug from power at any time, you can leave it on the charger for days if you wish, you can charge while the phone is on, you can charge while the phone is off. It doesn't matter.

Stedman