Uploading sketch to a Pro Mini on battery power

Currently I can upload sketches to the Pro Mini using my UNO (without chip). I plan to have the Pro Mini run on battery, in a sealed enclosure and be able to upload sketches too. The problem is how to do it while it's running on battery? I only connected the TX, RX, RST & Gnd (not the Vcc), to my UNO but I can't upload sketches.

I'm not sure if it's possible or I'm missing a connection, but is it possible to program the mini while it's on a battery (if so how?)

All the Arduinos need a VCC supply. Battery needs to be able to supply enough voltage and current to operate the on board voltage regulators.

Not quite enough detail in your question to give much more of a reply so maybe a schematic would help even if its hand drawn.

on my pro mini there is a 3.7 LIPO battery connected to RAW & GND

my UNO to mini connections (without battery) is

UNO -> Pro Mini (3.3V 8Mhz) (First 4 pin on top row of the mini)

0 (RX) -> 1 (RX) 1 (TX) -> 0 (TX) RESET -> RST GND -> GND 3.3V -> VCC

This works, I can upload sketches. But with battery connected, I only connected the first 4 (omitting the 3.3V to VCC) which does not work. Sketches tries to upload but progress bar just hangs at 100%

EDIT: nvr mind. I just tried it again and for some reason it works. Problem solved!