The CMOS battery has maybe 100mA and lasts 5 years. A laptop battery has at least 400x the capacity, it would not drain in a few days.

That won’t solve the software side. My previous phone was still working, but then Google fucked up the software. The first because it required some new ssl standard for all connections that the phone didn’t support. The other one because google added a whole lot of local Infos, pictures and features to the map that could not be disabled, therefore rendering my Navi to a unresponsive, slow and battery draining app I could no longer use. And then there where some apps that would not run because my os was to old.

This would be a bad approach, because you are essentially trying to brute force your way around a roadblock (no supported open data format) the supermarket intentionally designed. It would be easy for them to block your bot with Captchas, rate limits or IP blocking or just sue you.

You don’t need AI for that. All it takes is some standardized markup like schema.org and a discoverable price list page that can be read and understood by everyone.

We already had something similar with RSS, where you subscribe to your favorite blogs and forums, and the RSS reader on your computer would tell you which sites have new posts, so you don’t need to scan all of them each day. For some reason people stopped using RSS, and instead published their stuff (or notifications about new posts) on Facebook, twitter etc.

The same system could be adapted for (grocery-) price lists. However the big brands would never do that, because then it would be very easy to discover which products suddenly got more expensive.