Advise how to deal with shops where electricity is lost. I only pay through a cash register. What is the alternative in such a case? Apart from paying in cash.

I don't see any problem with that, because this is the twenty-first century and technology is developing exponentially. And haven't you heard that you can accept payments through certain apps on your phone, through nfs. It's a very cool thing. We have recently started using such a service and have almost given up on cash registers. You can read about the soft pos terminal here https://m4bank.com/softpos