We don't offer replacement keys at this time, but they are generically available Reention keys, made be Reention. There are a few 3rd party websites that offer replacement Reention keys for Reention battery systems. Here is one of the popular choices for ordering replacement keys: https://flx.bike/products/keys
You will need to know your 3-digit lock cylinder number (as pictured below). Just add your lock cylinder number in the order notes wherever you order the keys. They do not need to know what brand bike you have, as long as you are ordering keys from a Reention supplier.