Additionally to what @lasvegas mentioned, you can just get these https://www.amazon.com/1-5MM-Female-Single-Connector-Wires/dp/B0738CV1LP. They’re what was found to work to connect a larger battery in this thread: Swapping out Battery for Larger Capacity Li-Ion?
Should just be able to solder two together, making sure to connect them together in the appropriate orientation so you don’t reverse the polarity. Then you can just use heat shrink tubing, kapton tape, or electrical tape around the exposed portion of the soldered wire so it doesn’t short.