Here's how I did it. There are probably many other ways. If you dare to follow these instructions and something goes wrong it's on you. But, please send pictures of the fire truck!

The principles included are probably compatible to most all ebikes. You should wire these in parallel, not in series.

I am not sponsored by any product mentioned in this video. No one gave me a discounted price, nor did they send me anything free. The opinions expressed are my own.

Additional Battery: https://www.amazon.com/dp/B09C1T688C?...

Dual Battery Parallel Controller: https://www.area13ebikes.com/collecti...

XT90S Connectors: https://www.amazon.com/dp/B0893CGLP7?...

12g Wire: https://www.amazon.com/dp/B01ABOPMEI?...