I think it's a little harsh to call my advice "dangerous".
I bought a lipo pack to use in an Etronix Pulse, I later bought a second hand Gemini II and looking at it I realised that if I carefully swapped the lipo leads to match the +ve and -ve on the Sanwa battery holder it might work.
Which it did. So I posted my experience to help the OP.
This is how mine came. Lipo plug is at top and original battery plug below (I marked the +ve and -ve on the handset for reference)
I am no electrical engineer, I am a civil engineer but I simply used djmcnz's logic that red replaces red and black replaces black. If Sanwa changed terminals some way through the handset's life it's news to me and it's certainly not unreasonable for me to assume that my Gemini II is the same as another Gemini II...
However, I would hope that most everyone on this RC racing site understands basic electrics and wiring colours, electrically trained or not, and if what they found didn't match the advice, could cope with the logic needed to adapt it to their situation.