Battery replacement on keys

Anyone got recommendations for how to get keys back working?

My e46 touring came with 4 spare keys, all unlock and lock the car using the key. But the batteries are gone in them so you can’t use the remote. My one working key is now on the way out. So that’s 5 dead keys. Which is crazy imo.

I went to a few places and told there’s nothing that can be done cause they are sealed units. Anyone had success finding a place?

I’m based in Melbourne, Australia.