Need some ideas on how to install the battery in a seat post without a specific mounting system.
Currently I have the battery wrapped in plastic bubble wrap and shoved in there. The bottom taped up with electrical tape, just in case the wrap doesnt hold it in place to prevent drop out.
I mean this works but seem like a botched job to be honest, would like to know what you guys did..... 3D printing does not apply, no accces to such equipment.

You can try a rubber holder https://it.aliexpress.com/item/1005010683833559.html maybe work better than bubble wrap

In a round 27.2 seatpost I've used a layer of the foam window sealing tape that comes with portable air conditioners. It held just fine with an LTwoo battery, took some force to pull it back out.

I've used lots of things. Foam works well. I've also used a piece of chainstay protector. Just make it tight enough and it won't come off. Wrapping about half of the battery in length makes it easier to insert and rotating when pushing helps too. If the foam you use is thick it doesn't have to go all around the battery on one side is enough too.

I used two pieces of anti-rattle foam hydraulic tubing with some spiral cable bundle wrap inside my aero profile seatpost.