10 - 30 minuten
I had very poor battery life and went to the "Genius" store who reset the phone but it didn't work. Ordered a replacement battery and when trying to install it, the first step in the instructions said to power down the phone - my phone would not power down-it just kept rebooting. A Google search said to clean the docking connector with alcohol, I did and phone is fixed. Crud in the connector can cause the CPU to never go into standby. Now I go 12 hours on 20% battery usage.
Cleaned the docking connector and that fixed the phone. The replacement battery was not used and is still in the box. The key to the problem came from the iFixit instructions to power down the phone and it wouldn't power down. I am happy with iFixit but I didn't end up using their product.
Under settings select General==>Usage==> scroll to the bottom and look at Standby and Usage times and if they are the same - clean the connector. Your battery might be OK and changing the battery with a new one will still be a problem if the CPU won't go into Standby