Possible to turn on iPhone 5S with no battery attached?

Hey out there!

I just bought a water damaged iPhone 5S in the hopes of reviving it.

To give you the background story, the phone was placed in a zip lock bag on a canoe trip, where some moisture got into the bag. After this, the phone stopped working.

I have disassembled the phone and cleaned the motherboard with 99% isopropyl alcohol for any corrosion. After reassembling the phone, the phone is still dead. The computer doesn’t detect it either.

I have tried turning on the phone using a power cord and keeping the battery disconnected as I am not sure if the battery is dead or not - but is this possible on a healthy phone?

My next step is to remove all EMI shields and cleaning under these, in the hope this might revive the phone.

If anyone else has some ideas, please let me know! :)