I own an alian aurora electric bike that I bought in 2009,I am currently trying to replace the 36v10ah battery but aren't having much success the company it was bought from have apparently stopped trading.e
If I remember correctly, the Aurora has a rear rack mounted battery?
Why not replace it with one that mounts inside the bike frame.
It would improve the handling, balance and weight distribution.
You might have to extend the controller power lead a little and solder the connections, but it's easy enough, even for beginners.