maybe ur 3gs is defect unit.. my 3gs battery can last long for 2 days standby and 7hrs of usage(games, app, safari+3G, wifi, mail, map+3G, sms, call). My standby time 1% batt = 2.5-3hrs..

This is my initial battery charging..

#1 - Buy the iPhone 3G. Do not use the iPhone 3G.
#2 - Initially charge your iPhone for 3 hours. I've read conflicting statements about this. To be safe, don't use your phone before letting it charge for 3 hours. Also, use your wall charger (avoid the computer charger).
#3 - Now it's time to calibrate your battery indicator. Let the iPhone's battery fully drain. Keep the iPhone off for five hours once drained, then fully charge your battery. Allow the battery to rest in the fully charged state for two hours. You may use your iPhone during this time as long as the iPhone is plugged in.
#4 - Repeat step #3 a maximum of three times if you feel your battery indicator is inaccurate.

copy paste from this LINK

for Everyday Charging i always let the 3gs batt fully drain by it self.. (standby at 5% batt and let the phone fully drain, at this point u can see the % will goes up and down and goes up again..) and i use wall charger..

i am using OS 3.01

This post has been edited by afizudin: Aug 27 2009, 03:30 PM