iPhone shut down, only powers on when connected to charger

hi i have an iphone 6 plus that only stayed on with charging wire even though the battery was showing as almost full . When i opened the phone the battery seemed to have expanded slightly (damaged most likely). Replaced the battery for a new one and it is now fine.

This sounds like you got water or damaged the Doc connector where the charger plugs into so its not charging the battery so when you unplug it just dies straight away. replace the doc connector and take it from there as the battery is next in line! i got one for a fiver on ebay!!!

"Try to clean the contact between the battery and the phone, press hard on that contact and power the phone with charger disconnected. if it powers on you can install a small plastic bumper on top of the contact and than n force the cover on it will crate some Pressure .

good luck"

i think you need to replace the battery connector.But you need to know about microsoldering.iFixit has a video series about microsoldering.They have a video that they replaced the iphone 4s battery connector.But with the iphone 4 the process is almost identical.

ITS the Battery...the reason why it's randomly turn off...the reason your having iTunes error is because when the phone goes to restart itself it will not because the battery giving you this error and battery's are real tricky almost everyone who sells battery's say oem or original but even Apple has a lot of complains about battery's...lithium battery's are out of date and Easley breakable but ohhh well there cheap to make!