I use this cable: I just found this on AliExpress: | 2 core PU spring spiral cable wire 18 AWG 3/4 core 17 15 13 awg power cable stretch 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 meters
https://a.aliexpress.com/_EHq3Rrg
2m 13AWG, 3 core. On the thin side but it works. I added around 1m 11 awg (4mm2) of a different cable to the motor.
I just found this on AliExpress: | High Flexible Silicone Rubber Power Cable 2/3/4/5/6/7/8 Cores Chemical Resistant Extreme Temperature Medical Sterilization Wire
https://a.aliexpress.com/_Ex7aify
This one is available with 3 cores, up to awg 9 (6mm2), you could coil it yourself.
I was aslo reluctant to use a 2.5mm2 cable for the motor as it is on the small side but you also have to consider weight. 4 or even 6mm2 is getting heavy. I tested it 3 times and I could not feel the cable to get hot. The connector also seems to hold up. Motor phase current max is set to 140A.
To connect the motor pod to the hip box cable, I built connectors from 5.5mm rc bullets.
Link to my build: Daniels assist (3rd build)