This is the battery holder for additional battery for Xiaomi M365 scooter.

It's designed for 6AH battery (other won't fit) - I've bought mine for 60USD with charger.

You will need also 6 x M5 screws. I've screw them directly in to the plastic case - it's more then enough. In this case you need 40mm long screws. Or you can add a nut (there is a place for the nut inside the case) - and then you will need 45mm long screws and nuts.

To connect additional battery - you should also get T-type socket with cable, Y splitter with XT30 plugs and additional XT30 connector.

It should look something like this:

BOM:

Battery: https://www.aliexpress.com/item/32886306017.html
Y XT30 splitter: https://www.aliexpress.com/item/32997848431.html (1 Female to 2 Male)
T type socket with cable (1m): https://www.aliexpress.com/item/32891898225.html
XT30 connector (get a pair).

You can, of course buy all plugs/connectors and solder it by yourself - this is just the easiest way I've found. You will only need to solder one XT30 connector.

Leaving battery connector outside, allows you to fast disconnect battery (if needed) and using Y splitter inside (not soldering directly) will allow you to restore scooter to the original wiring if you would need that.

Warning!

Before connecting two batteries together, make sure they are at the same voltage level - just charge them fully.
After connecting them together, charge them both with original charger over the m365 charge socket (it's not perfect - but this will work, and make sure that batteries are balanced enough).