AR750S and AR750 How to always keep Update Lists (packages) after shut off

Hello! I’m sorry if this question is already asked, I’ve searched but did not found anywhere.

Every time I shut off the routers, I have to update manually package lists, so I think maybe there is a way to download all the packages to a SD or USB memory attached to the AR750S or AR750 directly from the router and add something in System/Software/Configuration? I tried dest mnt / USB or SD Card (example) but I think is just for installing packages, right?
Adding some lines in /etc/opkg.conf. maybe? But I don’t know what to add.

Thx

Yes it work like this. But why you want to keep the list.

Does it take too long to fetch the list?

The list could be saved to your browser (as in firmware v2.x) but v3.0 changed.