I also have the EXACT same problem! Unit was working fine, replaced battery, now it will not charge it. My mistake was letting it drain completely before attempting to charge it, but I bet my voltage readings are the same too. I am suspecting firmware 3.0 does it, but I have absolutely nothing to back up that theory with and now I will have to go back to my original battery and make sure that it is still charging with that one! Please let me know if you find a solution...
Edit: Confirmed, my voltage readings are the same.
It is possible that there is a firmware failsafe built into the phone starting with 3.0 that it will flag any catastrophic power events, IE NO BATTERY, and no longer allow the phone to charge. Restoring should fix that though, unless it was not a completely restore...or what I am thinking of trying is going to 2.X firmware to see if that fixes it. There were no other problems mentioned with this until the 3.0 firmware. I may be getting ahead of myself, first I have to make sure that my old battery won't work either, and then go from there. I also am wondering if it would be hard to charge these batteries outside of the phone, ie power supply until the solution can be found.
Well, I tried my original battery and it will no longer work. Therefore, I believe it is a safe assumption to say that there is some sort of detection and or flag in the firmware that detects a new battery and will not allow it to charge. This is most likely not a hardware flag because if it was, I believe that this problem would have cropped up by now for other people before firmware 3.0 and after searching the net I do not believe it has. Meaning that this failsafe or flag is new to 3.x firmware most likely and can probably be solved by having a battery with a full charge on it installed into the phone, and then restoring the phone with a 2.0 firmware. That is my hope anyway. I am going to talk to a guy who know Li-Ion batteries like the back of his hand about charging these batteries outside the phone, and then I plan on making an attempt at it. I'll post back tomorrow after I try it.
Spoke with the expert about these Lithium Polymer batteries and there is a Negative Temperature Compensation circuit included in the battery which is what the white wire is. The black wire is ground obviously and the red is positive. To charge this, as with all lithium ion batteries, it should be attached to a current limiting power supply with the current limter set to 1C of the battery in this case being about 1400mA. I will set mine to slightly less 1200mA just to be safe. The red wire on the power supply should be hooked to the red wire on the battery, the white wire should stay disconnected, and the black wire should be hooked to black on the power supply. Set the charge voltage on the power supply to 4.1 volts and turn it on and the battery should start to charge and the current used should begin to drop. Battery should be charged in about an hour and a half. This is all for a 1450mAh battery (iphone 2g replacement battery). I'll go ahead and try it and post results. Also after talking with the expert, it is very likely that Apple set a catastrophic battery flag in the new 3.x firmware. Restoring to a 2.X firmware should clear the flag. This is still speculation until proven.+
Well, I have succesfully recharged my battery using the method above and have installed it back in the phone and the phone registered it as being charged to 75%. Then I went to downgrade it and realized that I need an old version of iTunes and probably more. Trying to get that 'more' tomorrow. There are guides I am going to follow to help me downgrade from 3.0 because it doesn't appear to be an easy process.
