20 - 30 Minuten
Battery was draining fairly rapidly in Sept / Oct 2011 after acquiring 3GS in Oct 2010.
When battery level got to about 25% it would shutdown without so much as an alert showing 20% or 10% battery life. When trying to startup iPhone, the battery level showed nearly gone with Red and the icon urging to plug in power source. After waiting about 5 min or so, a successful iPhone startup (without plugging into power source) showed about 25%-33% good battery life. Of course, the whole process would repeat itself within a matter of minutes.
Decided it was about time for a new battery. :(
The repair went very well. It all started with the order online; very easy. Then the shipment; it arrived on time in excellent packaging.
The online fixit guide was very helpful. The photos were crisp and clear; the hiRes shots are invaluable. Success at last with a brand new (OEM looking) battery that has better charge, lasts longer, and now I get the std 20% and 10% battery level warnings again. :)
Yes, take the plunge. It is quite fun and rewarding to replace a 3GS battery for 20 bucks and about 15 min of hard labour! ;)
Although, be careful of connector #3 (flat ribbon cable that controls earpiece speaker, proximity sensor, and ambient light sensor). You could screw it up if you aren't careful.