[Martik777]

https://www.ebay.com/itm/2-5-10pc-T...hash=item4d56bf9cd4:m:mHm3Qdqm7PTMmvQGL2okUAg

Could I splice the output of this PCB to charge my phone with the battery connected to the motherboard? It will charge the phone if I disconnect the battery but I'm concerned it may damage the phone's board if connected while charging. It's a Moto G4

I don't want to chance damaging the board re-soldering a new micro usb port.

 

[FrodoOne]

After viewing your post and the link that it contains I still wonder what it is about which you are speaking or trying to do - for good or (probably) ill.

 

[chandler48]

A moto is aged at best. The worst you can do is mess it up. Then buy a more modern phone, or replace the G4. They only cost $75 or less on Amazon.

 

[Martik777]

After viewing your post and the link that it contains I still wonder what it is about which you are speaking or trying to do - for good or (probably) ill.

The TP4056 chipset is designed to charge a single cell li-ion battery. I normally use these for charging 18650's with a USB power source, but it will work with any li-ion cell.
See datasheet: https://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdf