Hello guys, I have an iphone 4 and unfortunately sometimes it turns off automatically even if the energy percentage of the battery is still very high. To turn it on I have to press the home button and the power button at the same time. Do you think the battery is leaving me and needs to be replaced? Or maybe the problem is something else? I've seen batteries on amazon and ebay. The price is very cheap and the reviews are mixed. I was looking for genuine ones but I don't seem to find them. One more thing : is there any part that could be replaced with parts from the iphone 4s just to upgrade it and make it more efficient. Your help would be very much appreciated.