Power issues - phone won't power on

Hi all,

I hope you can offer some insight into a recently purchased iPhone 5s I bought to repair.

The phone shows no sign of life when charging cable is plugged in ie no backlight, no Apple logo or charging icon is displayed. Also, there is no vibrate when it is given power via a mains charger.

I've opened the phone which appears to have been opened before. It shows no signs of water damage.

Using voltmeter, battery shows approx 0.2 volts when disconnected from logic board, clearly no enough to power on. I've also verified that no current is drawn when plugged in via an apple usb mains charger.

Question is - if I disconnect the battery from the logic board, and plug the lightening cable into the phone should it start? Just to clarify, can an iPhone 5s start without a battery plugged to the logic board?

The fact it's been opened before leads me to believe it's not just simple a case of replacing the battery or charge port since I imagine this would have been the 1st port of call (and a simple fix).

Any thoughts would be appreciated.

Cheers,

Jason.